/Src/Dependencies/Boost/libs/iterator/doc/facade-and-adaptor.html

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  7. <title>Iterator Facade and Adaptor</title>
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  8. <meta name="author" content="David Abrahams, Jeremy Siek, Thomas Witt" />
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  9. <meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab, Zephyr Associates, Inc." />
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  10. <meta name="date" content="2006-09-11" />
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  14. <div class="document" id="iterator-facade-and-adaptor">
    15. 

  15. <h1 class="title">Iterator Facade and Adaptor</h1>
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  16. <table class="docinfo" frame="void" rules="none">
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  17. <col class="docinfo-name" />
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  18. <col class="docinfo-content" />
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  19. <tbody valign="top">
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  20. <tr><th class="docinfo-name">Author:</th>
    21. 

  21. <td>David Abrahams, Jeremy Siek, Thomas Witt</td></tr>
    22. 

  22. <tr><th class="docinfo-name">Contact:</th>
    23. 

  23. <td><a class="first reference external" href="mailto:dave&#64;boost-consulting.com">dave&#64;boost-consulting.com</a>, <a class="reference external" href="mailto:jsiek&#64;osl.iu.edu">jsiek&#64;osl.iu.edu</a>, <a class="last reference external" href="mailto:witt&#64;styleadvisor.com">witt&#64;styleadvisor.com</a></td></tr>
    24. 

  24. <tr><th class="docinfo-name">Organization:</th>
    25. 

  25. <td><a class="first reference external" href="http://www.boost-consulting.com">Boost Consulting</a>, Indiana University <a class="reference external" href="http://www.osl.iu.edu">Open Systems
    26. 

  26. Lab</a>, <a class="last reference external" href="http://www.styleadvisor.com">Zephyr Associates, Inc.</a></td></tr>
    27. 

  27. <tr><th class="docinfo-name">Date:</th>
    28. 

  28. <td>2006-09-11</td></tr>
    29. 

  29. <tr class="field"><th class="docinfo-name">Number:</th><td class="field-body">This is a revised version of <a class="reference external" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1530.html">N1530</a>=03-0113, which was
    30. 

  30. accepted for Technical Report 1 by the C++ standard
    31. 

  31. committee's library working group.</td>
    32. 

  32. </tr>
    33. 

  33. </tbody>
    34. 

  34. </table>
    35. 

  35. <!-- Distributed under the Boost -->
    36. 

  36. <!-- Software License, Version 1.0. (See accompanying -->
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  37. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    38. 

  38. <!-- Version 1.9 of this ReStructuredText document corresponds to
    39. 

  39. n1530_, the paper accepted by the LWG. -->
    40. 

  40. <table class="docutils field-list" frame="void" rules="none">
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  41. <col class="field-name" />
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  42. <col class="field-body" />
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  43. <tbody valign="top">
    44. 

  44. <tr class="field"><th class="field-name">copyright:</th><td class="field-body">Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003.</td>
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  45. </tr>
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  46. </tbody>
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  47. </table>
    48. 

  48. <table class="docutils field-list" frame="void" rules="none">
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  49. <col class="field-name" />
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  50. <col class="field-body" />
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  51. <tbody valign="top">
    52. 

  52. <tr class="field"><th class="field-name">abstract:</th><td class="field-body">We propose a set of class templates that help programmers
    53. 

  53. build standard-conforming iterators, both from scratch and
    54. 

  54. by adapting other iterators.</td>
    55. 

  55. </tr>
    56. 

  56. </tbody>
    57. 

  57. </table>
    58. 

  58. <div class="contents topic" id="table-of-contents">
    59. 

  59. <p class="topic-title first">Table of Contents</p>
    60. 

  60. <ul class="simple">
    61. 

  61. <li><a class="reference internal" href="#motivation" id="id15">Motivation</a></li>
    62. 

  62. <li><a class="reference internal" href="#impact-on-the-standard" id="id16">Impact on the Standard</a></li>
    63. 

  63. <li><a class="reference internal" href="#design" id="id17">Design</a><ul>
    64. 

  64. <li><a class="reference internal" href="#iterator-concepts" id="id18">Iterator Concepts</a></li>
    65. 

  65. <li><a class="reference internal" href="#interoperability" id="id19">Interoperability</a></li>
    66. 

  66. <li><a class="reference internal" href="#iterator-facade" id="id20">Iterator Facade</a><ul>
    67. 

  67. <li><a class="reference internal" href="#usage" id="id21">Usage</a></li>
    68. 

  68. <li><a class="reference internal" href="#iterator-core-access" id="id22">Iterator Core Access</a></li>
    69. 

  69. <li><a class="reference internal" href="#operator" id="id23"><tt class="docutils literal"><span class="pre">operator[]</span></tt></a></li>
    70. 

  70. <li><a class="reference internal" href="#id6" id="id24"><tt class="docutils literal"><span class="pre">operator-&gt;</span></tt></a></li>
    71. 

  71. </ul>
    72. 

  72. </li>
    73. 

  73. <li><a class="reference internal" href="#iterator-adaptor" id="id25">Iterator Adaptor</a></li>
    74. 

  74. <li><a class="reference internal" href="#specialized-adaptors" id="id26">Specialized Adaptors</a></li>
    75. 

  75. </ul>
    76. 

  76. </li>
    77. 

  77. <li><a class="reference internal" href="#proposed-text" id="id27">Proposed Text</a><ul>
    78. 

  78. <li><a class="reference internal" href="#header-iterator-helper-synopsis-lib-iterator-helper-synopsis" id="id28">Header <tt class="docutils literal"><span class="pre">&lt;iterator_helper&gt;</span></tt> synopsis    [lib.iterator.helper.synopsis]</a></li>
    79. 

  79. <li><a class="reference internal" href="#iterator-facade-lib-iterator-facade" id="id29">Iterator facade [lib.iterator.facade]</a><ul>
    80. 

  80. <li><a class="reference internal" href="#class-template-iterator-facade" id="id30">Class template <tt class="docutils literal"><span class="pre">iterator_facade</span></tt></a></li>
    81. 

  81. <li><a class="reference internal" href="#iterator-facade-requirements" id="id31"><tt class="docutils literal"><span class="pre">iterator_facade</span></tt> Requirements</a></li>
    82. 

  82. <li><a class="reference internal" href="#iterator-facade-operations" id="id32"><tt class="docutils literal"><span class="pre">iterator_facade</span></tt> operations</a></li>
    83. 

  83. </ul>
    84. 

  84. </li>
    85. 

  85. <li><a class="reference internal" href="#iterator-adaptor-lib-iterator-adaptor" id="id33">Iterator adaptor [lib.iterator.adaptor]</a><ul>
    86. 

  86. <li><a class="reference internal" href="#class-template-iterator-adaptor" id="id34">Class template <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt></a></li>
    87. 

  87. <li><a class="reference internal" href="#iterator-adaptor-requirements" id="id35"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> requirements</a></li>
    88. 

  88. <li><a class="reference internal" href="#iterator-adaptor-base-class-parameters" id="id36"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> base class parameters</a></li>
    89. 

  89. <li><a class="reference internal" href="#iterator-adaptor-public-operations" id="id37"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> public operations</a></li>
    90. 

  90. <li><a class="reference internal" href="#iterator-adaptor-protected-member-functions" id="id38"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> protected member functions</a></li>
    91. 

  91. <li><a class="reference internal" href="#iterator-adaptor-private-member-functions" id="id39"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> private member functions</a></li>
    92. 

  92. </ul>
    93. 

  93. </li>
    94. 

  94. <li><a class="reference internal" href="#specialized-adaptors-lib-iterator-special-adaptors" id="id40">Specialized adaptors [lib.iterator.special.adaptors]</a><ul>
    95. 

  95. <li><a class="reference internal" href="#indirect-iterator" id="id41">Indirect iterator</a><ul>
    96. 

  96. <li><a class="reference internal" href="#class-template-pointee" id="id42">Class template <tt class="docutils literal"><span class="pre">pointee</span></tt></a></li>
    97. 

  97. <li><a class="reference internal" href="#class-template-indirect-reference" id="id43">Class template <tt class="docutils literal"><span class="pre">indirect_reference</span></tt></a></li>
    98. 

  98. <li><a class="reference internal" href="#class-template-indirect-iterator" id="id44">Class template <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt></a></li>
    99. 

  99. <li><a class="reference internal" href="#indirect-iterator-requirements" id="id45"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> requirements</a></li>
    100. 

  100. <li><a class="reference internal" href="#indirect-iterator-models" id="id46"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> models</a></li>
    101. 

  101. <li><a class="reference internal" href="#indirect-iterator-operations" id="id47"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> operations</a></li>
    102. 

  102. </ul>
    103. 

  103. </li>
    104. 

  104. <li><a class="reference internal" href="#reverse-iterator" id="id48">Reverse iterator</a><ul>
    105. 

  105. <li><a class="reference internal" href="#class-template-reverse-iterator" id="id49">Class template <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt></a></li>
    106. 

  106. <li><a class="reference internal" href="#reverse-iterator-requirements" id="id50"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> requirements</a></li>
    107. 

  107. <li><a class="reference internal" href="#reverse-iterator-models" id="id51"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> models</a></li>
    108. 

  108. <li><a class="reference internal" href="#reverse-iterator-operations" id="id52"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> operations</a></li>
    109. 

  109. </ul>
    110. 

  110. </li>
    111. 

  111. <li><a class="reference internal" href="#transform-iterator" id="id53">Transform iterator</a><ul>
    112. 

  112. <li><a class="reference internal" href="#class-template-transform-iterator" id="id54">Class template <tt class="docutils literal"><span class="pre">transform_iterator</span></tt></a></li>
    113. 

  113. <li><a class="reference internal" href="#transform-iterator-requirements" id="id55"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> requirements</a></li>
    114. 

  114. <li><a class="reference internal" href="#transform-iterator-models" id="id56"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models</a></li>
    115. 

  115. <li><a class="reference internal" href="#transform-iterator-operations" id="id57"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> operations</a></li>
    116. 

  116. </ul>
    117. 

  117. </li>
    118. 

  118. <li><a class="reference internal" href="#filter-iterator" id="id58">Filter iterator</a><ul>
    119. 

  119. <li><a class="reference internal" href="#class-template-filter-iterator" id="id59">Class template <tt class="docutils literal"><span class="pre">filter_iterator</span></tt></a></li>
    120. 

  120. <li><a class="reference internal" href="#filter-iterator-requirements" id="id60"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> requirements</a></li>
    121. 

  121. <li><a class="reference internal" href="#filter-iterator-models" id="id61"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</a></li>
    122. 

  122. <li><a class="reference internal" href="#filter-iterator-operations" id="id62"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> operations</a></li>
    123. 

  123. </ul>
    124. 

  124. </li>
    125. 

  125. <li><a class="reference internal" href="#counting-iterator" id="id63">Counting iterator</a><ul>
    126. 

  126. <li><a class="reference internal" href="#class-template-counting-iterator" id="id64">Class template <tt class="docutils literal"><span class="pre">counting_iterator</span></tt></a></li>
    127. 

  127. <li><a class="reference internal" href="#counting-iterator-requirements" id="id65"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> requirements</a></li>
    128. 

  128. <li><a class="reference internal" href="#counting-iterator-models" id="id66"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models</a></li>
    129. 

  129. <li><a class="reference internal" href="#counting-iterator-operations" id="id67"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> operations</a></li>
    130. 

  130. </ul>
    131. 

  131. </li>
    132. 

  132. <li><a class="reference internal" href="#function-output-iterator" id="id68">Function output iterator</a><ul>
    133. 

  133. <li><a class="reference internal" href="#class-template-function-output-iterator" id="id69">Class template <tt class="docutils literal"><span class="pre">function_output_iterator</span></tt></a></li>
    134. 

  134. <li><a class="reference internal" href="#header" id="id70">Header</a></li>
    135. 

  135. <li><a class="reference internal" href="#function-output-iterator-requirements" id="id71"><tt class="docutils literal"><span class="pre">function_output_iterator</span></tt> requirements</a></li>
    136. 

  136. <li><a class="reference internal" href="#function-output-iterator-models" id="id72"><tt class="docutils literal"><span class="pre">function_output_iterator</span></tt> models</a></li>
    137. 

  137. <li><a class="reference internal" href="#function-output-iterator-operations" id="id73"><tt class="docutils literal"><span class="pre">function_output_iterator</span></tt> operations</a></li>
    138. 

  138. </ul>
    139. 

  139. </li>
    140. 

  140. </ul>
    141. 

  141. </li>
    142. 

  142. </ul>
    143. 

  143. </li>
    144. 

  144. </ul>
    145. 

  145. </div>
    146. 

  146. <div class="section" id="motivation">
    147. 

  147. <h1><a class="toc-backref" href="#id15">Motivation</a></h1>
    148. 

  148. <p>Iterators play an important role in modern C++ programming. The
    149. 

  149. iterator is the central abstraction of the algorithms of the Standard
    150. 

  150. Library, allowing algorithms to be re-used in in a wide variety of
    151. 

  151. contexts.  The C++ Standard Library contains a wide variety of useful
    152. 

  152. iterators. Every one of the standard containers comes with constant
    153. 

  153. and mutable iterators<a class="footnote-reference" href="#mutable" id="id1"><sup>2</sup></a>, and also reverse versions of those
    154. 

  154. same iterators which traverse the container in the opposite direction.
    155. 

  155. The Standard also supplies <tt class="docutils literal"><span class="pre">istream_iterator</span></tt> and
    156. 

  156. <tt class="docutils literal"><span class="pre">ostream_iterator</span></tt> for reading from and writing to streams,
    157. 

  157. <tt class="docutils literal"><span class="pre">insert_iterator</span></tt>, <tt class="docutils literal"><span class="pre">front_insert_iterator</span></tt> and
    158. 

  158. <tt class="docutils literal"><span class="pre">back_insert_iterator</span></tt> for inserting elements into containers, and
    159. 

  159. <tt class="docutils literal"><span class="pre">raw_storage_iterator</span></tt> for initializing raw memory [7].</p>
    160. 

  160. <p>Despite the many iterators supplied by the Standard Library, obvious
    161. 

  161. and useful iterators are missing, and creating new iterator types is
    162. 

  162. still a common task for C++ programmers.  The literature documents
    163. 

  163. several of these, for example line_iterator [3] and Constant_iterator
    164. 

  164. [9].  The iterator abstraction is so powerful that we expect
    165. 

  165. programmers will always need to invent new iterator types.</p>
    166. 

  166. <p>Although it is easy to create iterators that <em>almost</em> conform to the
    167. 

  167. standard, the iterator requirements contain subtleties which can make
    168. 

  168. creating an iterator which <em>actually</em> conforms quite difficult.
    169. 

  169. Further, the iterator interface is rich, containing many operators
    170. 

  170. that are technically redundant and tedious to implement.  To automate
    171. 

  171. the repetitive work of constructing iterators, we propose
    172. 

  172. <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>, an iterator base class template which provides
    173. 

  173. the rich interface of standard iterators and delegates its
    174. 

  174. implementation to member functions of the derived class.  In addition
    175. 

  175. to reducing the amount of code necessary to create an iterator, the
    176. 

  176. <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> also provides compile-time error detection.
    177. 

  177. Iterator implementation mistakes that often go unnoticed are turned
    178. 

  178. into compile-time errors because the derived class implementation must
    179. 

  179. match the expectations of the <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>.</p>
    180. 

  180. <p>A common pattern of iterator construction is the adaptation of one
    181. 

  181. iterator to form a new one.  The functionality of an iterator is
    182. 

  182. composed of four orthogonal aspects: traversal, indirection, equality
    183. 

  183. comparison and distance measurement.  Adapting an old iterator to
    184. 

  184. create a new one often saves work because one can reuse one aspect of
    185. 

  185. functionality while redefining the other.  For example, the Standard
    186. 

  186. provides <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt>, which adapts any Bidirectional Iterator
    187. 

  187. by inverting its direction of traversal.  As with plain iterators,
    188. 

  188. iterator adaptors defined outside the Standard have become commonplace
    189. 

  189. in the literature:</p>
    190. 

  190. <ul class="simple">
    191. 

  191. <li>Checked iter[13] adds bounds-checking to an existing iterator.</li>
    192. 

  192. <li>The iterators of the View Template Library[14], which adapts
    193. 

  193. containers, are themselves adaptors over the underlying iterators.</li>
    194. 

  194. <li>Smart iterators [5] adapt an iterator's dereferencing behavior by
    195. 

  195. applying a function object to the object being referenced and
    196. 

  196. returning the result.</li>
    197. 

  197. <li>Custom iterators [4], in which a variety of adaptor types are enumerated.</li>
    198. 

  198. <li>Compound iterators [1], which access a slice out of a container of containers.</li>
    199. 

  199. <li>Several iterator adaptors from the MTL [12].  The MTL contains a
    200. 

  200. strided iterator, where each call to <tt class="docutils literal"><span class="pre">operator++()</span></tt> moves the
    201. 

  201. iterator ahead by some constant factor, and a scaled iterator, which
    202. 

  202. multiplies the dereferenced value by some constant.</li>
    203. 

  203. </ul>
    204. 

  204. <table class="docutils footnote" frame="void" id="concept" rules="none">
    205. 

  205. <colgroup><col class="label" /><col /></colgroup>
    206. 

  206. <tbody valign="top">
    207. 

  207. <tr><td class="label">[1]</td><td>We use the term concept to mean a set of requirements
    208. 

  208. that a type must satisfy to be used with a particular template
    209. 

  209. parameter.</td></tr>
    210. 

  210. </tbody>
    211. 

  211. </table>
    212. 

  212. <table class="docutils footnote" frame="void" id="mutable" rules="none">
    213. 

  213. <colgroup><col class="label" /><col /></colgroup>
    214. 

  214. <tbody valign="top">
    215. 

  215. <tr><td class="label"><a class="fn-backref" href="#id1">[2]</a></td><td>The term mutable iterator refers to iterators over objects that
    216. 

  216. can be changed by assigning to the dereferenced iterator, while
    217. 

  217. constant iterator refers to iterators over objects that cannot be
    218. 

  218. modified.</td></tr>
    219. 

  219. </tbody>
    220. 

  220. </table>
    221. 

  221. <p>To fulfill the need for constructing adaptors, we propose the
    222. 

  222. <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> class template.  Instantiations of
    223. 

  223. <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> serve as a base classes for new iterators,
    224. 

  224. providing the default behavior of forwarding all operations to the
    225. 

  225. underlying iterator.  The user can selectively replace these features
    226. 

  226. in the derived iterator class.  This proposal also includes a number
    227. 

  227. of more specialized adaptors, such as the <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> that
    228. 

  228. applies some user-specified function during the dereference of the
    229. 

  229. iterator.</p>
    230. 

  230. </div>
    231. 

  231. <div class="section" id="impact-on-the-standard">
    232. 

  232. <h1><a class="toc-backref" href="#id16">Impact on the Standard</a></h1>
    233. 

  233. <p>This proposal is purely an addition to the C++ standard library.
    234. 

  234. However, note that this proposal relies on the proposal for New
    235. 

  235. Iterator Concepts.</p>
    236. 

  236. </div>
    237. 

  237. <div class="section" id="design">
    238. 

  238. <h1><a class="toc-backref" href="#id17">Design</a></h1>
    239. 

  239. <div class="section" id="iterator-concepts">
    240. 

  240. <h2><a class="toc-backref" href="#id18">Iterator Concepts</a></h2>
    241. 

  241. <p>This proposal is formulated in terms of the new <tt class="docutils literal"><span class="pre">iterator</span> <span class="pre">concepts</span></tt>
    242. 

  242. as proposed in <a class="reference external" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html">n1550</a>, since user-defined and especially adapted
    243. 

  243. iterators suffer from the well known categorization problems that are
    244. 

  244. inherent to the current iterator categories.</p>
    245. 

  245. <p>This proposal does not strictly depend on proposal <a class="reference external" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html">n1550</a>, as there
    246. 

  246. is a direct mapping between new and old categories. This proposal
    247. 

  247. could be reformulated using this mapping if <a class="reference external" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html">n1550</a> was not accepted.</p>
    248. 

  248. </div>
    249. 

  249. <div class="section" id="interoperability">
    250. 

  250. <h2><a class="toc-backref" href="#id19">Interoperability</a></h2>
    251. 

  251. <p>The question of iterator interoperability is poorly addressed in the
    252. 

  252. current standard.  There are currently two defect reports that are
    253. 

  253. concerned with interoperability issues.</p>
    254. 

  254. <p>Issue <a class="reference external" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#179">179</a> concerns the fact that mutable container iterator types
    255. 

  255. are only required to be convertible to the corresponding constant
    256. 

  256. iterator types, but objects of these types are not required to
    257. 

  257. interoperate in comparison or subtraction expressions.  This situation
    258. 

  258. is tedious in practice and out of line with the way built in types
    259. 

  259. work.  This proposal implements the proposed resolution to issue
    260. 

  260. <a class="reference external" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#179">179</a>, as most standard library implementations do nowadays. In other
    261. 

  261. words, if an iterator type A has an implicit or user defined
    262. 

  262. conversion to an iterator type B, the iterator types are interoperable
    263. 

  263. and the usual set of operators are available.</p>
    264. 

  264. <p>Issue <a class="reference external" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-active.html#280">280</a> concerns the current lack of interoperability between
    265. 

  265. reverse iterator types. The proposed new reverse_iterator template
    266. 

  266. fixes the issues raised in 280. It provides the desired
    267. 

  267. interoperability without introducing unwanted overloads.</p>
    268. 

  268. </div>
    269. 

  269. <div class="section" id="iterator-facade">
    270. 

  270. <h2><a class="toc-backref" href="#id20">Iterator Facade</a></h2>
    271. 

  271. <!-- Distributed under the Boost -->
    272. 

  272. <!-- Software License, Version 1.0. (See accompanying -->
    273. 

  273. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    274. 

  274. <!-- Version 1.1 of this ReStructuredText document corresponds to
    275. 

  275. n1530_, the paper accepted by the LWG for TR1. -->
    276. 

  276. <!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. -->
    277. 

  277. <p>While the iterator interface is rich, there is a core subset of the
    278. 

  278. interface that is necessary for all the functionality.  We have
    279. 

  279. identified the following core behaviors for iterators:</p>
    280. 

  280. <ul class="simple">
    281. 

  281. <li>dereferencing</li>
    282. 

  282. <li>incrementing</li>
    283. 

  283. <li>decrementing</li>
    284. 

  284. <li>equality comparison</li>
    285. 

  285. <li>random-access motion</li>
    286. 

  286. <li>distance measurement</li>
    287. 

  287. </ul>
    288. 

  288. <p>In addition to the behaviors listed above, the core interface elements
    289. 

  289. include the associated types exposed through iterator traits:
    290. 

  290. <tt class="docutils literal"><span class="pre">value_type</span></tt>, <tt class="docutils literal"><span class="pre">reference</span></tt>, <tt class="docutils literal"><span class="pre">difference_type</span></tt>, and
    291. 

  291. <tt class="docutils literal"><span class="pre">iterator_category</span></tt>.</p>
    292. 

  292. <p>Iterator facade uses the Curiously Recurring Template
    293. 

  293. Pattern (CRTP) <a class="citation-reference" href="#cop95" id="id4">[Cop95]</a> so that the user can specify the behavior
    294. 

  294. of <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> in a derived class.  Former designs used
    295. 

  295. policy objects to specify the behavior, but that approach was
    296. 

  296. discarded for several reasons:</p>
    297. 

  297. <blockquote>
    298. 

  298. <ol class="arabic simple">
    299. 

  299. <li>the creation and eventual copying of the policy object may create
    300. 

  300. overhead that can be avoided with the current approach.</li>
    301. 

  301. <li>The policy object approach does not allow for custom constructors
    302. 

  302. on the created iterator types, an essential feature if
    303. 

  303. <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> should be used in other library
    304. 

  304. implementations.</li>
    305. 

  305. <li>Without the use of CRTP, the standard requirement that an
    306. 

  306. iterator's <tt class="docutils literal"><span class="pre">operator++</span></tt> returns the iterator type itself
    307. 

  307. would mean that all iterators built with the library would
    308. 

  308. have to be specializations of <tt class="docutils literal"><span class="pre">iterator_facade&lt;...&gt;</span></tt>, rather
    309. 

  309. than something more descriptive like
    310. 

  310. <tt class="docutils literal"><span class="pre">indirect_iterator&lt;T*&gt;</span></tt>.  Cumbersome type generator
    311. 

  311. metafunctions would be needed to build new parameterized
    312. 

  312. iterators, and a separate <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> layer would be
    313. 

  313. impossible.</li>
    314. 

  314. </ol>
    315. 

  315. </blockquote>
    316. 

  316. <div class="section" id="usage">
    317. 

  317. <h3><a class="toc-backref" href="#id21">Usage</a></h3>
    318. 

  318. <p>The user of <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> derives his iterator class from a
    319. 

  319. specialization of <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> and passes the derived
    320. 

  320. iterator class as <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>'s first template parameter.
    321. 

  321. The order of the other template parameters have been carefully
    322. 

  322. chosen to take advantage of useful defaults.  For example, when
    323. 

  323. defining a constant lvalue iterator, the user can pass a
    324. 

  324. const-qualified version of the iterator's <tt class="docutils literal"><span class="pre">value_type</span></tt> as
    325. 

  325. <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>'s <tt class="docutils literal"><span class="pre">Value</span></tt> parameter and omit the
    326. 

  326. <tt class="docutils literal"><span class="pre">Reference</span></tt> parameter which follows.</p>
    327. 

  327. <p>The derived iterator class must define member functions implementing
    328. 

  328. the iterator's core behaviors.  The following table describes
    329. 

  329. expressions which are required to be valid depending on the category
    330. 

  330. of the derived iterator type.  These member functions are described
    331. 

  331. briefly below and in more detail in the iterator facade
    332. 

  332. requirements.</p>
    333. 

  333. <blockquote>
    334. 

  334. <table border="1" class="docutils">
    335. 

  335. <colgroup>
    336. 

  336. <col width="44%" />
    337. 

  337. <col width="56%" />
    338. 

  338. </colgroup>
    339. 

  339. <thead valign="bottom">
    340. 

  340. <tr><th class="head">Expression</th>
    341. 

  341. <th class="head">Effects</th>
    342. 

  342. </tr>
    343. 

  343. </thead>
    344. 

  344. <tbody valign="top">
    345. 

  345. <tr><td><tt class="docutils literal"><span class="pre">i.dereference()</span></tt></td>
    346. 

  346. <td>Access the value referred to</td>
    347. 

  347. </tr>
    348. 

  348. <tr><td><tt class="docutils literal"><span class="pre">i.equal(j)</span></tt></td>
    349. 

  349. <td>Compare for equality with <tt class="docutils literal"><span class="pre">j</span></tt></td>
    350. 

  350. </tr>
    351. 

  351. <tr><td><tt class="docutils literal"><span class="pre">i.increment()</span></tt></td>
    352. 

  352. <td>Advance by one position</td>
    353. 

  353. </tr>
    354. 

  354. <tr><td><tt class="docutils literal"><span class="pre">i.decrement()</span></tt></td>
    355. 

  355. <td>Retreat by one position</td>
    356. 

  356. </tr>
    357. 

  357. <tr><td><tt class="docutils literal"><span class="pre">i.advance(n)</span></tt></td>
    358. 

  358. <td>Advance by <tt class="docutils literal"><span class="pre">n</span></tt> positions</td>
    359. 

  359. </tr>
    360. 

  360. <tr><td><tt class="docutils literal"><span class="pre">i.distance_to(j)</span></tt></td>
    361. 

  361. <td>Measure the distance to <tt class="docutils literal"><span class="pre">j</span></tt></td>
    362. 

  362. </tr>
    363. 

  363. </tbody>
    364. 

  364. </table>
    365. 

  365. </blockquote>
    366. 

  366. <!-- Should we add a comment that a zero overhead implementation of iterator_facade
    367. 

  367. is possible with proper inlining? -->
    368. 

  368. <p>In addition to implementing the core interface functions, an iterator
    369. 

  369. derived from <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> typically defines several
    370. 

  370. constructors. To model any of the standard iterator concepts, the
    371. 

  371. iterator must at least have a copy constructor. Also, if the iterator
    372. 

  372. type <tt class="docutils literal"><span class="pre">X</span></tt> is meant to be automatically interoperate with another
    373. 

  373. iterator type <tt class="docutils literal"><span class="pre">Y</span></tt> (as with constant and mutable iterators) then
    374. 

  374. there must be an implicit conversion from <tt class="docutils literal"><span class="pre">X</span></tt> to <tt class="docutils literal"><span class="pre">Y</span></tt> or from <tt class="docutils literal"><span class="pre">Y</span></tt>
    375. 

  375. to <tt class="docutils literal"><span class="pre">X</span></tt> (but not both), typically implemented as a conversion
    376. 

  376. constructor. Finally, if the iterator is to model Forward Traversal
    377. 

  377. Iterator or a more-refined iterator concept, a default constructor is
    378. 

  378. required.</p>
    379. 

  379. </div>
    380. 

  380. <div class="section" id="iterator-core-access">
    381. 

  381. <h3><a class="toc-backref" href="#id22">Iterator Core Access</a></h3>
    382. 

  382. <p><tt class="docutils literal"><span class="pre">iterator_facade</span></tt> and the operator implementations need to be able
    383. 

  383. to access the core member functions in the derived class.  Making the
    384. 

  384. core member functions public would expose an implementation detail to
    385. 

  385. the user.  The design used here ensures that implementation details do
    386. 

  386. not appear in the public interface of the derived iterator type.</p>
    387. 

  387. <p>Preventing direct access to the core member functions has two
    388. 

  388. advantages.  First, there is no possibility for the user to accidently
    389. 

  389. use a member function of the iterator when a member of the value_type
    390. 

  390. was intended.  This has been an issue with smart pointer
    391. 

  391. implementations in the past.  The second and main advantage is that
    392. 

  392. library implementers can freely exchange a hand-rolled iterator
    393. 

  393. implementation for one based on <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> without fear of
    394. 

  394. breaking code that was accessing the public core member functions
    395. 

  395. directly.</p>
    396. 

  396. <p>In a naive implementation, keeping the derived class' core member
    397. 

  397. functions private would require it to grant friendship to
    398. 

  398. <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> and each of the seven operators.  In order to
    399. 

  399. reduce the burden of limiting access, <tt class="docutils literal"><span class="pre">iterator_core_access</span></tt> is
    400. 

  400. provided, a class that acts as a gateway to the core member functions
    401. 

  401. in the derived iterator class.  The author of the derived class only
    402. 

  402. needs to grant friendship to <tt class="docutils literal"><span class="pre">iterator_core_access</span></tt> to make his core
    403. 

  403. member functions available to the library.</p>
    404. 

  404. <!-- This is no long uptodate -thw -->
    405. 

  405. <!-- Yes it is; I made sure of it! -DWA -->
    406. 

  406. <p><tt class="docutils literal"><span class="pre">iterator_core_access</span></tt> will be typically implemented as an empty
    407. 

  407. class containing only private static member functions which invoke the
    408. 

  408. iterator core member functions. There is, however, no need to
    409. 

  409. standardize the gateway protocol.  Note that even if
    410. 

  410. <tt class="docutils literal"><span class="pre">iterator_core_access</span></tt> used public member functions it would not
    411. 

  411. open a safety loophole, as every core member function preserves the
    412. 

  412. invariants of the iterator.</p>
    413. 

  413. </div>
    414. 

  414. <div class="section" id="operator">
    415. 

  415. <h3><a class="toc-backref" href="#id23"><tt class="docutils literal"><span class="pre">operator[]</span></tt></a></h3>
    416. 

  416. <p>The indexing operator for a generalized iterator presents special
    417. 

  417. challenges.  A random access iterator's <tt class="docutils literal"><span class="pre">operator[]</span></tt> is only
    418. 

  418. required to return something convertible to its <tt class="docutils literal"><span class="pre">value_type</span></tt>.
    419. 

  419. Requiring that it return an lvalue would rule out currently-legal
    420. 

  420. random-access iterators which hold the referenced value in a data
    421. 

  421. member (e.g. <a class="reference internal" href="#counting"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt></a>), because <tt class="docutils literal"><span class="pre">*(p+n)</span></tt> is a reference
    422. 

  422. into the temporary iterator <tt class="docutils literal"><span class="pre">p+n</span></tt>, which is destroyed when
    423. 

  423. <tt class="docutils literal"><span class="pre">operator[]</span></tt> returns.</p>
    424. 

  424. <p>Writable iterators built with <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> implement the
    425. 

  425. semantics required by the preferred resolution to <a class="reference external" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-active.html#299">issue 299</a> and
    426. 

  426. adopted by proposal <a class="reference external" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html">n1550</a>: the result of <tt class="docutils literal"><span class="pre">p[n]</span></tt> is an object
    427. 

  427. convertible to the iterator's <tt class="docutils literal"><span class="pre">value_type</span></tt>, and <tt class="docutils literal"><span class="pre">p[n]</span> <span class="pre">=</span> <span class="pre">x</span></tt> is
    428. 

  428. equivalent to <tt class="docutils literal"><span class="pre">*(p</span> <span class="pre">+</span> <span class="pre">n)</span> <span class="pre">=</span> <span class="pre">x</span></tt> (Note: This result object may be
    429. 

  429. implemented as a proxy containing a copy of <tt class="docutils literal"><span class="pre">p+n</span></tt>).  This approach
    430. 

  430. will work properly for any random-access iterator regardless of the
    431. 

  431. other details of its implementation.  A user who knows more about
    432. 

  432. the implementation of her iterator is free to implement an
    433. 

  433. <tt class="docutils literal"><span class="pre">operator[]</span></tt> that returns an lvalue in the derived iterator
    434. 

  434. class; it will hide the one supplied by <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> from
    435. 

  435. clients of her iterator.</p>
    436. 

  436. </div>
    437. 

  437. <div class="section" id="id6">
    438. 

  438. <span id="operator-arrow"></span><h3><a class="toc-backref" href="#id24"><tt class="docutils literal"><span class="pre">operator-&gt;</span></tt></a></h3>
    439. 

  439. <p>The <tt class="docutils literal"><span class="pre">reference</span></tt> type of a readable iterator (and today's input
    440. 

  440. iterator) need not in fact be a reference, so long as it is
    441. 

  441. convertible to the iterator's <tt class="docutils literal"><span class="pre">value_type</span></tt>.  When the <tt class="docutils literal"><span class="pre">value_type</span></tt>
    442. 

  442. is a class, however, it must still be possible to access members
    443. 

  443. through <tt class="docutils literal"><span class="pre">operator-&gt;</span></tt>.  Therefore, an iterator whose <tt class="docutils literal"><span class="pre">reference</span></tt>
    444. 

  444. type is not in fact a reference must return a proxy containing a copy
    445. 

  445. of the referenced value from its <tt class="docutils literal"><span class="pre">operator-&gt;</span></tt>.</p>
    446. 

  446. <p>The return types for <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>'s <tt class="docutils literal"><span class="pre">operator-&gt;</span></tt> and
    447. 

  447. <tt class="docutils literal"><span class="pre">operator[]</span></tt> are not explicitly specified. Instead, those types
    448. 

  448. are described in terms of a set of requirements, which must be
    449. 

  449. satisfied by the <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> implementation.</p>
    450. 

  450. <table class="docutils citation" frame="void" id="cop95" rules="none">
    451. 

  451. <colgroup><col class="label" /><col /></colgroup>
    452. 

  452. <tbody valign="top">
    453. 

  453. <tr><td class="label"><a class="fn-backref" href="#id4">[Cop95]</a></td><td>[Coplien, 1995] Coplien, J., Curiously Recurring Template
    454. 

  454. Patterns, C++ Report, February 1995, pp. 24-27.</td></tr>
    455. 

  455. </tbody>
    456. 

  456. </table>
    457. 

  457. </div>
    458. 

  458. </div>
    459. 

  459. <div class="section" id="iterator-adaptor">
    460. 

  460. <h2><a class="toc-backref" href="#id25">Iterator Adaptor</a></h2>
    461. 

  461. <!-- Distributed under the Boost -->
    462. 

  462. <!-- Software License, Version 1.0. (See accompanying -->
    463. 

  463. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    464. 

  464. <!-- Version 1.2 of this ReStructuredText document corresponds to
    465. 

  465. n1530_, the paper accepted by the LWG for TR1. -->
    466. 

  466. <!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. -->
    467. 

  467. <p>The <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> class template adapts some <tt class="docutils literal"><span class="pre">Base</span></tt><a class="footnote-reference" href="#base" id="id7"><sup>3</sup></a>
    468. 

  468. type to create a new iterator.  Instantiations of <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt>
    469. 

  469. are derived from a corresponding instantiation of <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>
    470. 

  470. and implement the core behaviors in terms of the <tt class="docutils literal"><span class="pre">Base</span></tt> type. In
    471. 

  471. essence, <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> merely forwards all operations to an
    472. 

  472. instance of the <tt class="docutils literal"><span class="pre">Base</span></tt> type, which it stores as a member.</p>
    473. 

  473. <table class="docutils footnote" frame="void" id="base" rules="none">
    474. 

  474. <colgroup><col class="label" /><col /></colgroup>
    475. 

  475. <tbody valign="top">
    476. 

  476. <tr><td class="label"><a class="fn-backref" href="#id7">[3]</a></td><td>The term &quot;Base&quot; here does not refer to a base class and is
    477. 

  477. not meant to imply the use of derivation. We have followed the lead
    478. 

  478. of the standard library, which provides a base() function to access
    479. 

  479. the underlying iterator object of a <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> adaptor.</td></tr>
    480. 

  480. </tbody>
    481. 

  481. </table>
    482. 

  482. <p>The user of <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> creates a class derived from an
    483. 

  483. instantiation of <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> and then selectively
    484. 

  484. redefines some of the core member functions described in the
    485. 

  485. <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> core requirements table. The <tt class="docutils literal"><span class="pre">Base</span></tt> type need
    486. 

  486. not meet the full requirements for an iterator; it need only
    487. 

  487. support the operations used by the core interface functions of
    488. 

  488. <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> that have not been redefined in the user's
    489. 

  489. derived class.</p>
    490. 

  490. <p>Several of the template parameters of <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> default
    491. 

  491. to <tt class="docutils literal"><span class="pre">use_default</span></tt>. This allows the
    492. 

  492. user to make use of a default parameter even when she wants to
    493. 

  493. specify a parameter later in the parameter list.  Also, the
    494. 

  494. defaults for the corresponding associated types are somewhat
    495. 

  495. complicated, so metaprogramming is required to compute them, and
    496. 

  496. <tt class="docutils literal"><span class="pre">use_default</span></tt> can help to simplify the implementation.  Finally,
    497. 

  497. the identity of the <tt class="docutils literal"><span class="pre">use_default</span></tt> type is not left unspecified
    498. 

  498. because specification helps to highlight that the <tt class="docutils literal"><span class="pre">Reference</span></tt>
    499. 

  499. template parameter may not always be identical to the iterator's
    500. 

  500. <tt class="docutils literal"><span class="pre">reference</span></tt> type, and will keep users from making mistakes based on
    501. 

  501. that assumption.</p>
    502. 

  502. </div>
    503. 

  503. <div class="section" id="specialized-adaptors">
    504. 

  504. <h2><a class="toc-backref" href="#id26">Specialized Adaptors</a></h2>
    505. 

  505. <p>This proposal also contains several examples of specialized adaptors
    506. 

  506. which were easily implemented using <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt>:</p>
    507. 

  507. <ul class="simple">
    508. 

  508. <li><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt>, which iterates over iterators, pointers,
    509. 

  509. or smart pointers and applies an extra level of dereferencing.</li>
    510. 

  510. <li>A new <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt>, which inverts the direction of a Base
    511. 

  511. iterator's motion, while allowing adapted constant and mutable
    512. 

  512. iterators to interact in the expected ways (unlike those in most
    513. 

  513. implementations of C++98).</li>
    514. 

  514. <li><tt class="docutils literal"><span class="pre">transform_iterator</span></tt>, which applies a user-defined function object
    515. 

  515. to the underlying values when dereferenced.</li>
    516. 

  516. <li><tt class="docutils literal"><span class="pre">filter_iterator</span></tt>, which provides a view of an iterator range in
    517. 

  517. which some elements of the underlying range are skipped.</li>
    518. 

  518. </ul>
    519. 

  519. <ul class="simple" id="counting">
    520. 

  520. <li><tt class="docutils literal"><span class="pre">counting_iterator</span></tt>, which adapts any incrementable type
    521. 

  521. (e.g. integers, iterators) so that incrementing/decrementing the
    522. 

  522. adapted iterator and dereferencing it produces successive values of
    523. 

  523. the Base type.</li>
    524. 

  524. <li><tt class="docutils literal"><span class="pre">function_output_iterator</span></tt>, which makes it easier to create custom
    525. 

  525. output iterators.</li>
    526. 

  526. </ul>
    527. 

  527. <p>Based on examples in the Boost library, users have generated many new
    528. 

  528. adaptors, among them a permutation adaptor which applies some
    529. 

  529. permutation to a random access iterator, and a strided adaptor, which
    530. 

  530. adapts a random access iterator by multiplying its unit of motion by a
    531. 

  531. constant factor.  In addition, the Boost Graph Library (BGL) uses
    532. 

  532. iterator adaptors to adapt other graph libraries, such as LEDA [10]
    533. 

  533. and Stanford GraphBase [8], to the BGL interface (which requires C++
    534. 

  534. Standard compliant iterators).</p>
    535. 

  535. </div>
    536. 

  536. </div>
    537. 

  537. <div class="section" id="proposed-text">
    538. 

  538. <h1><a class="toc-backref" href="#id27">Proposed Text</a></h1>
    539. 

  539. <div class="section" id="header-iterator-helper-synopsis-lib-iterator-helper-synopsis">
    540. 

  540. <h2><a class="toc-backref" href="#id28">Header <tt class="docutils literal"><span class="pre">&lt;iterator_helper&gt;</span></tt> synopsis    [lib.iterator.helper.synopsis]</a></h2>
    541. 

  541. <pre class="literal-block">
    542. 

  542. struct use_default;
    543. 

  543. 

  544. struct iterator_core_access { /* implementation detail */ };
    545. 

  545. 

  546. template &lt;
    547. 

  547.     class Derived
    548. 

  548.   , class Value
    549. 

  549.   , class CategoryOrTraversal
    550. 

  550.   , class Reference  = Value&amp;
    551. 

  551.   , class Difference = ptrdiff_t
    552. 

  552. &gt;
    553. 

  553. class iterator_facade;
    554. 

  554. 

  555. template &lt;
    556. 

  556.     class Derived
    557. 

  557.   , class Base
    558. 

  558.   , class Value      = use_default
    559. 

  559.   , class CategoryOrTraversal  = use_default
    560. 

  560.   , class Reference  = use_default
    561. 

  561.   , class Difference = use_default
    562. 

  562. &gt;
    563. 

  563. class iterator_adaptor;
    564. 

  564. 

  565. template &lt;
    566. 

  566.     class Iterator
    567. 

  567.   , class Value = use_default
    568. 

  568.   , class CategoryOrTraversal = use_default
    569. 

  569.   , class Reference = use_default
    570. 

  570.   , class Difference = use_default
    571. 

  571. &gt;
    572. 

  572. class indirect_iterator;
    573. 

  573. 

  574. template &lt;class Dereferenceable&gt;
    575. 

  575. struct pointee;
    576. 

  576. 

  577. template &lt;class Dereferenceable&gt;
    578. 

  578. struct indirect_reference;
    579. 

  579. 

  580. template &lt;class Iterator&gt;
    581. 

  581. class reverse_iterator;
    582. 

  582. 

  583. template &lt;
    584. 

  584.     class UnaryFunction
    585. 

  585.   , class Iterator
    586. 

  586.   , class Reference = use_default
    587. 

  587.   , class Value = use_default
    588. 

  588. &gt;
    589. 

  589. class transform_iterator;
    590. 

  590. 

  591. template &lt;class Predicate, class Iterator&gt;
    592. 

  592. class filter_iterator;
    593. 

  593. 

  594. template &lt;
    595. 

  595.     class Incrementable
    596. 

  596.   , class CategoryOrTraversal  = use_default
    597. 

  597.   , class Difference = use_default
    598. 

  598. &gt;
    599. 

  599. class counting_iterator;
    600. 

  600. 

  601. template &lt;class UnaryFunction&gt;
    602. 

  602. class function_output_iterator;
    603. 

  603. </pre>
    604. 

  604. </div>
    605. 

  605. <div class="section" id="iterator-facade-lib-iterator-facade">
    606. 

  606. <h2><a class="toc-backref" href="#id29">Iterator facade [lib.iterator.facade]</a></h2>
    607. 

  607. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    608. 

  608. <!-- Software License, Version 1.0. (See accompanying -->
    609. 

  609. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    610. 

  610. <p><tt class="docutils literal"><span class="pre">iterator_facade</span></tt> is a base class template that implements the
    611. 

  611. interface of standard iterators in terms of a few core functions
    612. 

  612. and associated types, to be supplied by a derived iterator class.</p>
    613. 

  613. <div class="section" id="class-template-iterator-facade">
    614. 

  614. <h3><a class="toc-backref" href="#id30">Class template <tt class="docutils literal"><span class="pre">iterator_facade</span></tt></a></h3>
    615. 

  615. <!-- Distributed under the Boost -->
    616. 

  616. <!-- Software License, Version 1.0. (See accompanying -->
    617. 

  617. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    618. 

  618. <!-- Version 1.3 of this ReStructuredText document corresponds to
    619. 

  619. n1530_, the paper accepted by the LWG for TR1. -->
    620. 

  620. <!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. -->
    621. 

  621. <pre class="literal-block">
    622. 

  622. template &lt;
    623. 

  623.     class Derived
    624. 

  624.   , class Value
    625. 

  625.   , class CategoryOrTraversal
    626. 

  626.   , class Reference  = Value&amp;
    627. 

  627.   , class Difference = ptrdiff_t
    628. 

  628. &gt;
    629. 

  629. class iterator_facade {
    630. 

  630.  public:
    631. 

  631.     typedef remove_const&lt;Value&gt;::type value_type;
    632. 

  632.     typedef Reference reference;
    633. 

  633.     typedef Value* pointer;
    634. 

  634.     typedef Difference difference_type;
    635. 

  635.     typedef /* see <a class="reference internal" href="#iterator-category">below</a> */ iterator_category;
    636. 

  636. 

  637.     reference operator*() const;
    638. 

  638.     /* see <a class="reference internal" href="#operator-arrow">below</a> */ operator-&gt;() const;
    639. 

  639.     /* see <a class="reference internal" href="#brackets">below</a> */ operator[](difference_type n) const;
    640. 

  640.     Derived&amp; operator++();
    641. 

  641.     Derived operator++(int);
    642. 

  642.     Derived&amp; operator--();
    643. 

  643.     Derived operator--(int);
    644. 

  644.     Derived&amp; operator+=(difference_type n);
    645. 

  645.     Derived&amp; operator-=(difference_type n);
    646. 

  646.     Derived operator-(difference_type n) const;
    647. 

  647.  protected:
    648. 

  648.     typedef iterator_facade iterator_facade_;
    649. 

  649. };
    650. 

  650. 

  651. // Comparison operators
    652. 

  652. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    653. 

  653.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    654. 

  654. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type // exposition
    655. 

  655. operator ==(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    656. 

  656.             iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    657. 

  657. 

  658. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    659. 

  659.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    660. 

  660. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    661. 

  661. operator !=(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    662. 

  662.             iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    663. 

  663. 

  664. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    665. 

  665.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    666. 

  666. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    667. 

  667. operator &lt;(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    668. 

  668.            iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    669. 

  669. 

  670. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    671. 

  671.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    672. 

  672. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    673. 

  673. operator &lt;=(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    674. 

  674.             iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    675. 

  675. 

  676. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    677. 

  677.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    678. 

  678. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    679. 

  679. operator &gt;(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    680. 

  680.            iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    681. 

  681. 

  682. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    683. 

  683.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    684. 

  684. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    685. 

  685. operator &gt;=(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    686. 

  686.             iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    687. 

  687. 

  688. // Iterator difference
    689. 

  689. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    690. 

  690.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    691. 

  691. /* see <a class="reference internal" href="#minus">below</a> */
    692. 

  692. operator-(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    693. 

  693.           iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    694. 

  694. 

  695. // Iterator addition
    696. 

  696. template &lt;class Dr, class V, class TC, class R, class D&gt;
    697. 

  697. Derived operator+ (iterator_facade&lt;Dr,V,TC,R,D&gt; const&amp;,
    698. 

  698.                    typename Derived::difference_type n);
    699. 

  699. 

  700. template &lt;class Dr, class V, class TC, class R, class D&gt;
    701. 

  701. Derived operator+ (typename Derived::difference_type n,
    702. 

  702.                    iterator_facade&lt;Dr,V,TC,R,D&gt; const&amp;);
    703. 

  703. </pre>
    704. 

  704. <p id="iterator-category">The <tt class="docutils literal"><span class="pre">iterator_category</span></tt> member of <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> is</p>
    705. 

  705. <pre class="literal-block">
    706. 

  706. <em>iterator-category</em>(CategoryOrTraversal, value_type, reference)
    707. 

  707. </pre>
    708. 

  708. <p>where <em>iterator-category</em> is defined as follows:</p>
    709. 

  709. <pre class="literal-block" id="id12">
    710. 

  710. <em>iterator-category</em>(C,R,V) :=
    711. 

  711.    if (C is convertible to std::input_iterator_tag
    712. 

  712.        || C is convertible to std::output_iterator_tag
    713. 

  713.    )
    714. 

  714.        return C
    715. 

  715. 

  716.    else if (C is not convertible to incrementable_traversal_tag)
    717. 

  717.        <em>the program is ill-formed</em>
    718. 

  718. 

  719.    else return a type X satisfying the following two constraints:
    720. 

  720. 

  721.       1. X is convertible to X1, and not to any more-derived
    722. 

  722.          type, where X1 is defined by:
    723. 

  723. 

  724.            if (R is a reference type
    725. 

  725.                &amp;&amp; C is convertible to forward_traversal_tag)
    726. 

  726.            {
    727. 

  727.                if (C is convertible to random_access_traversal_tag)
    728. 

  728.                    X1 = random_access_iterator_tag
    729. 

  729.                else if (C is convertible to bidirectional_traversal_tag)
    730. 

  730.                    X1 = bidirectional_iterator_tag
    731. 

  731.                else
    732. 

  732.                    X1 = forward_iterator_tag
    733. 

  733.            }
    734. 

  734.            else
    735. 

  735.            {
    736. 

  736.                if (C is convertible to single_pass_traversal_tag
    737. 

  737.                    &amp;&amp; R is convertible to V)
    738. 

  738.                    X1 = input_iterator_tag
    739. 

  739.                else
    740. 

  740.                    X1 = C
    741. 

  741.            }
    742. 

  742. 

  743.       2. <a class="reference external" href="new-iter-concepts.html#category-to-traversal"><em>category-to-traversal</em></a>(X) is convertible to the most
    744. 

  744.          derived traversal tag type to which X is also
    745. 

  745.          convertible, and not to any more-derived traversal tag
    746. 

  746.          type.
    747. 

  747. </pre>
    748. 

  748. <p>[Note: the intention is to allow <tt class="docutils literal"><span class="pre">iterator_category</span></tt> to be one of
    749. 

  749. the five original category tags when convertibility to one of the
    750. 

  750. traversal tags would add no information]</p>
    751. 

  751. <!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
    752. 

  752. <!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
    753. 

  753. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    754. 

  754. <p>The <tt class="docutils literal"><span class="pre">enable_if_interoperable</span></tt> template used above is for exposition
    755. 

  755. purposes.  The member operators should only be in an overload set
    756. 

  756. provided the derived types <tt class="docutils literal"><span class="pre">Dr1</span></tt> and <tt class="docutils literal"><span class="pre">Dr2</span></tt> are interoperable,
    757. 

  757. meaning that at least one of the types is convertible to the other.  The
    758. 

  758. <tt class="docutils literal"><span class="pre">enable_if_interoperable</span></tt> approach uses SFINAE to take the operators
    759. 

  759. out of the overload set when the types are not interoperable.
    760. 

  760. The operators should behave <em>as-if</em> <tt class="docutils literal"><span class="pre">enable_if_interoperable</span></tt>
    761. 

  761. were defined to be:</p>
    762. 

  762. <pre class="literal-block">
    763. 

  763. template &lt;bool, typename&gt; enable_if_interoperable_impl
    764. 

  764. {};
    765. 

  765. 

  766. template &lt;typename T&gt; enable_if_interoperable_impl&lt;true,T&gt;
    767. 

  767. { typedef T type; };
    768. 

  768. 

  769. template&lt;typename Dr1, typename Dr2, typename T&gt;
    770. 

  770. struct enable_if_interoperable
    771. 

  771.   : enable_if_interoperable_impl&lt;
    772. 

  772.         is_convertible&lt;Dr1,Dr2&gt;::value || is_convertible&lt;Dr2,Dr1&gt;::value
    773. 

  773.       , T
    774. 

  774.     &gt;
    775. 

  775. {};
    776. 

  776. </pre>
    777. 

  777. </div>
    778. 

  778. <div class="section" id="iterator-facade-requirements">
    779. 

  779. <h3><a class="toc-backref" href="#id31"><tt class="docutils literal"><span class="pre">iterator_facade</span></tt> Requirements</a></h3>
    780. 

  780. <p>The following table describes the typical valid expressions on
    781. 

  781. <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>'s <tt class="docutils literal"><span class="pre">Derived</span></tt> parameter, depending on the
    782. 

  782. iterator concept(s) it will model.  The operations in the first
    783. 

  783. column must be made accessible to member functions of class
    784. 

  784. <tt class="docutils literal"><span class="pre">iterator_core_access</span></tt>.  In addition,
    785. 

  785. <tt class="docutils literal"><span class="pre">static_cast&lt;Derived*&gt;(iterator_facade*)</span></tt> shall be well-formed.</p>
    786. 

  786. <p>In the table below, <tt class="docutils literal"><span class="pre">F</span></tt> is <tt class="docutils literal"><span class="pre">iterator_facade&lt;X,V,C,R,D&gt;</span></tt>, <tt class="docutils literal"><span class="pre">a</span></tt> is an
    787. 

  787. object of type <tt class="docutils literal"><span class="pre">X</span></tt>, <tt class="docutils literal"><span class="pre">b</span></tt> and <tt class="docutils literal"><span class="pre">c</span></tt> are objects of type <tt class="docutils literal"><span class="pre">const</span> <span class="pre">X</span></tt>,
    788. 

  788. <tt class="docutils literal"><span class="pre">n</span></tt> is an object of <tt class="docutils literal"><span class="pre">F::difference_type</span></tt>, <tt class="docutils literal"><span class="pre">y</span></tt> is a constant
    789. 

  789. object of a single pass iterator type interoperable with <tt class="docutils literal"><span class="pre">X</span></tt>, and <tt class="docutils literal"><span class="pre">z</span></tt>
    790. 

  790. is a constant object of a random access traversal iterator type
    791. 

  791. interoperable with <tt class="docutils literal"><span class="pre">X</span></tt>.</p>
    792. 

  792. <div class="topic" id="core-operations">
    793. 

  793. <p class="topic-title first"><tt class="docutils literal"><span class="pre">iterator_facade</span></tt> Core Operations</p>
    794. 

  794. <table border="1" class="docutils">
    795. 

  795. <colgroup>
    796. 

  796. <col width="21%" />
    797. 

  797. <col width="23%" />
    798. 

  798. <col width="27%" />
    799. 

  799. <col width="29%" />
    800. 

  800. </colgroup>
    801. 

  801. <thead valign="bottom">
    802. 

  802. <tr><th class="head">Expression</th>
    803. 

  803. <th class="head">Return Type</th>
    804. 

  804. <th class="head">Assertion/Note</th>
    805. 

  805. <th class="head">Used to implement Iterator
    806. 

  806. Concept(s)</th>
    807. 

  807. </tr>
    808. 

  808. </thead>
    809. 

  809. <tbody valign="top">
    810. 

  810. <tr><td><tt class="docutils literal"><span class="pre">c.dereference()</span></tt></td>
    811. 

  811. <td><tt class="docutils literal"><span class="pre">F::reference</span></tt></td>
    812. 

  812. <td>&nbsp;</td>
    813. 

  813. <td>Readable Iterator, Writable
    814. 

  814. Iterator</td>
    815. 

  815. </tr>
    816. 

  816. <tr><td><tt class="docutils literal"><span class="pre">c.equal(y)</span></tt></td>
    817. 

  817. <td>convertible to bool</td>
    818. 

  818. <td>true iff <tt class="docutils literal"><span class="pre">c</span></tt> and <tt class="docutils literal"><span class="pre">y</span></tt>
    819. 

  819. refer to the same
    820. 

  820. position.</td>
    821. 

  821. <td>Single Pass Iterator</td>
    822. 

  822. </tr>
    823. 

  823. <tr><td><tt class="docutils literal"><span class="pre">a.increment()</span></tt></td>
    824. 

  824. <td>unused</td>
    825. 

  825. <td>&nbsp;</td>
    826. 

  826. <td>Incrementable Iterator</td>
    827. 

  827. </tr>
    828. 

  828. <tr><td><tt class="docutils literal"><span class="pre">a.decrement()</span></tt></td>
    829. 

  829. <td>unused</td>
    830. 

  830. <td>&nbsp;</td>
    831. 

  831. <td>Bidirectional Traversal
    832. 

  832. Iterator</td>
    833. 

  833. </tr>
    834. 

  834. <tr><td><tt class="docutils literal"><span class="pre">a.advance(n)</span></tt></td>
    835. 

  835. <td>unused</td>
    836. 

  836. <td>&nbsp;</td>
    837. 

  837. <td>Random Access Traversal
    838. 

  838. Iterator</td>
    839. 

  839. </tr>
    840. 

  840. <tr><td><tt class="docutils literal"><span class="pre">c.distance_to(z)</span></tt></td>
    841. 

  841. <td>convertible to
    842. 

  842. <tt class="docutils literal"><span class="pre">F::difference_type</span></tt></td>
    843. 

  843. <td>equivalent to
    844. 

  844. <tt class="docutils literal"><span class="pre">distance(c,</span> <span class="pre">X(z))</span></tt>.</td>
    845. 

  845. <td>Random Access Traversal
    846. 

  846. Iterator</td>
    847. 

  847. </tr>
    848. 

  848. </tbody>
    849. 

  849. </table>
    850. 

  850. </div>
    851. 

  851. </div>
    852. 

  852. <div class="section" id="iterator-facade-operations">
    853. 

  853. <h3><a class="toc-backref" href="#id32"><tt class="docutils literal"><span class="pre">iterator_facade</span></tt> operations</a></h3>
    854. 

  854. <p>The operations in this section are described in terms of operations on
    855. 

  855. the core interface of <tt class="docutils literal"><span class="pre">Derived</span></tt> which may be inaccessible
    856. 

  856. (i.e. private).  The implementation should access these operations
    857. 

  857. through member functions of class <tt class="docutils literal"><span class="pre">iterator_core_access</span></tt>.</p>
    858. 

  858. <p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
    859. 

  859. <table class="docutils field-list" frame="void" rules="none">
    860. 

  860. <col class="field-name" />
    861. 

  861. <col class="field-body" />
    862. 

  862. <tbody valign="top">
    863. 

  863. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">static_cast&lt;Derived</span> <span class="pre">const*&gt;(this)-&gt;dereference()</span></tt></td>
    864. 

  864. </tr>
    865. 

  865. </tbody>
    866. 

  866. </table>
    867. 

  867. <p><tt class="docutils literal"><span class="pre">operator-&gt;()</span> <span class="pre">const;</span></tt> (see <a class="reference internal" href="#operator-arrow">below</a>)</p>
    868. 

  868. <table class="docutils field-list" frame="void" rules="none">
    869. 

  869. <col class="field-name" />
    870. 

  870. <col class="field-body" />
    871. 

  871. <tbody valign="top">
    872. 

  872. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">If <tt class="docutils literal"><span class="pre">reference</span></tt> is a reference type, an object
    873. 

  873. of type <tt class="docutils literal"><span class="pre">pointer</span></tt> equal to:</p>
    874. 

  874. <pre class="literal-block">
    875. 

  875. &amp;static_cast&lt;Derived const*&gt;(this)-&gt;dereference()
    876. 

  876. </pre>
    877. 

  877. <p class="last">Otherwise returns an object of unspecified type such that,
    878. 

  878. <tt class="docutils literal"><span class="pre">(*static_cast&lt;Derived</span> <span class="pre">const*&gt;(this))-&gt;m</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">(w</span> <span class="pre">=</span> <span class="pre">**static_cast&lt;Derived</span> <span class="pre">const*&gt;(this),</span>
    879. 

  879. <span class="pre">w.m)</span></tt> for some temporary object <tt class="docutils literal"><span class="pre">w</span></tt> of type <tt class="docutils literal"><span class="pre">value_type</span></tt>.</p>
    880. 

  880. </td>
    881. 

  881. </tr>
    882. 

  882. </tbody>
    883. 

  883. </table>
    884. 

  884. <p id="brackets"><em>unspecified</em> <tt class="docutils literal"><span class="pre">operator[](difference_type</span> <span class="pre">n)</span> <span class="pre">const;</span></tt></p>
    885. 

  885. <table class="docutils field-list" frame="void" rules="none">
    886. 

  886. <col class="field-name" />
    887. 

  887. <col class="field-body" />
    888. 

  888. <tbody valign="top">
    889. 

  889. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">an object convertible to <tt class="docutils literal"><span class="pre">value_type</span></tt>. For constant
    890. 

  890. objects <tt class="docutils literal"><span class="pre">v</span></tt> of type <tt class="docutils literal"><span class="pre">value_type</span></tt>, and <tt class="docutils literal"><span class="pre">n</span></tt> of type
    891. 

  891. <tt class="docutils literal"><span class="pre">difference_type</span></tt>, <tt class="docutils literal"><span class="pre">(*this)[n]</span> <span class="pre">=</span> <span class="pre">v</span></tt> is equivalent to
    892. 

  892. <tt class="docutils literal"><span class="pre">*(*this</span> <span class="pre">+</span> <span class="pre">n)</span> <span class="pre">=</span> <span class="pre">v</span></tt>, and <tt class="docutils literal"><span class="pre">static_cast&lt;value_type</span>
    893. 

  893. <span class="pre">const&amp;&gt;((*this)[n])</span></tt> is equivalent to
    894. 

  894. <tt class="docutils literal"><span class="pre">static_cast&lt;value_type</span> <span class="pre">const&amp;&gt;(*(*this</span> <span class="pre">+</span> <span class="pre">n))</span></tt></td>
    895. 

  895. </tr>
    896. 

  896. </tbody>
    897. 

  897. </table>
    898. 

  898. <p><tt class="docutils literal"><span class="pre">Derived&amp;</span> <span class="pre">operator++();</span></tt></p>
    899. 

  899. <table class="docutils field-list" frame="void" rules="none">
    900. 

  900. <col class="field-name" />
    901. 

  901. <col class="field-body" />
    902. 

  902. <tbody valign="top">
    903. 

  903. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><pre class="first last literal-block">
    904. 

  904. static_cast&lt;Derived*&gt;(this)-&gt;increment();
    905. 

  905. return *static_cast&lt;Derived*&gt;(this);
    906. 

  906. </pre>
    907. 

  907. </td>
    908. 

  908. </tr>
    909. 

  909. </tbody>
    910. 

  910. </table>
    911. 

  911. <p><tt class="docutils literal"><span class="pre">Derived</span> <span class="pre">operator++(int);</span></tt></p>
    912. 

  912. <table class="docutils field-list" frame="void" rules="none">
    913. 

  913. <col class="field-name" />
    914. 

  914. <col class="field-body" />
    915. 

  915. <tbody valign="top">
    916. 

  916. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><pre class="first last literal-block">
    917. 

  917. Derived tmp(static_cast&lt;Derived const*&gt;(this));
    918. 

  918. ++*this;
    919. 

  919. return tmp;
    920. 

  920. </pre>
    921. 

  921. </td>
    922. 

  922. </tr>
    923. 

  923. </tbody>
    924. 

  924. </table>
    925. 

  925. <p><tt class="docutils literal"><span class="pre">Derived&amp;</span> <span class="pre">operator--();</span></tt></p>
    926. 

  926. <table class="docutils field-list" frame="void" rules="none">
    927. 

  927. <col class="field-name" />
    928. 

  928. <col class="field-body" />
    929. 

  929. <tbody valign="top">
    930. 

  930. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><pre class="first last literal-block">
    931. 

  931. static_cast&lt;Derived*&gt;(this)-&gt;decrement();
    932. 

  932. return *static_cast&lt;Derived*&gt;(this);
    933. 

  933. </pre>
    934. 

  934. </td>
    935. 

  935. </tr>
    936. 

  936. </tbody>
    937. 

  937. </table>
    938. 

  938. <p><tt class="docutils literal"><span class="pre">Derived</span> <span class="pre">operator--(int);</span></tt></p>
    939. 

  939. <table class="docutils field-list" frame="void" rules="none">
    940. 

  940. <col class="field-name" />
    941. 

  941. <col class="field-body" />
    942. 

  942. <tbody valign="top">
    943. 

  943. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><pre class="first last literal-block">
    944. 

  944. Derived tmp(static_cast&lt;Derived const*&gt;(this));
    945. 

  945. --*this;
    946. 

  946. return tmp;
    947. 

  947. </pre>
    948. 

  948. </td>
    949. 

  949. </tr>
    950. 

  950. </tbody>
    951. 

  951. </table>
    952. 

  952. <p><tt class="docutils literal"><span class="pre">Derived&amp;</span> <span class="pre">operator+=(difference_type</span> <span class="pre">n);</span></tt></p>
    953. 

  953. <table class="docutils field-list" frame="void" rules="none">
    954. 

  954. <col class="field-name" />
    955. 

  955. <col class="field-body" />
    956. 

  956. <tbody valign="top">
    957. 

  957. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><pre class="first last literal-block">
    958. 

  958. static_cast&lt;Derived*&gt;(this)-&gt;advance(n);
    959. 

  959. return *static_cast&lt;Derived*&gt;(this);
    960. 

  960. </pre>
    961. 

  961. </td>
    962. 

  962. </tr>
    963. 

  963. </tbody>
    964. 

  964. </table>
    965. 

  965. <p><tt class="docutils literal"><span class="pre">Derived&amp;</span> <span class="pre">operator-=(difference_type</span> <span class="pre">n);</span></tt></p>
    966. 

  966. <table class="docutils field-list" frame="void" rules="none">
    967. 

  967. <col class="field-name" />
    968. 

  968. <col class="field-body" />
    969. 

  969. <tbody valign="top">
    970. 

  970. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><pre class="first last literal-block">
    971. 

  971. static_cast&lt;Derived*&gt;(this)-&gt;advance(-n);
    972. 

  972. return *static_cast&lt;Derived*&gt;(this);
    973. 

  973. </pre>
    974. 

  974. </td>
    975. 

  975. </tr>
    976. 

  976. </tbody>
    977. 

  977. </table>
    978. 

  978. <p><tt class="docutils literal"><span class="pre">Derived</span> <span class="pre">operator-(difference_type</span> <span class="pre">n)</span> <span class="pre">const;</span></tt></p>
    979. 

  979. <table class="docutils field-list" frame="void" rules="none">
    980. 

  980. <col class="field-name" />
    981. 

  981. <col class="field-body" />
    982. 

  982. <tbody valign="top">
    983. 

  983. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><pre class="first last literal-block">
    984. 

  984. Derived tmp(static_cast&lt;Derived const*&gt;(this));
    985. 

  985. return tmp -= n;
    986. 

  986. </pre>
    987. 

  987. </td>
    988. 

  988. </tr>
    989. 

  989. </tbody>
    990. 

  990. </table>
    991. 

  991. <pre class="literal-block">
    992. 

  992. template &lt;class Dr, class V, class TC, class R, class D&gt;
    993. 

  993. Derived operator+ (iterator_facade&lt;Dr,V,TC,R,D&gt; const&amp;,
    994. 

  994.                    typename Derived::difference_type n);
    995. 

  995. 

  996. template &lt;class Dr, class V, class TC, class R, class D&gt;
    997. 

  997. Derived operator+ (typename Derived::difference_type n,
    998. 

  998.                    iterator_facade&lt;Dr,V,TC,R,D&gt; const&amp;);
    999. 

  999. </pre>
    1000. 

  1000. <table class="docutils field-list" frame="void" rules="none">
    1001. 

  1001. <col class="field-name" />
    1002. 

  1002. <col class="field-body" />
    1003. 

  1003. <tbody valign="top">
    1004. 

  1004. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><pre class="first last literal-block">
    1005. 

  1005. Derived tmp(static_cast&lt;Derived const*&gt;(this));
    1006. 

  1006. return tmp += n;
    1007. 

  1007. </pre>
    1008. 

  1008. </td>
    1009. 

  1009. </tr>
    1010. 

  1010. </tbody>
    1011. 

  1011. </table>
    1012. 

  1012. <pre class="literal-block">
    1013. 

  1013. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    1014. 

  1014.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    1015. 

  1015. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    1016. 

  1016. operator ==(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    1017. 

  1017.             iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    1018. 

  1018. </pre>
    1019. 

  1019. <table class="docutils field-list" frame="void" rules="none">
    1020. 

  1020. <col class="field-name" />
    1021. 

  1021. <col class="field-body" />
    1022. 

  1022. <tbody valign="top">
    1023. 

  1023. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">if <tt class="docutils literal"><span class="pre">is_convertible&lt;Dr2,Dr1&gt;::value</span></tt></p>
    1024. 

  1024. <dl class="last docutils">
    1025. 

  1025. <dt>then</dt>
    1026. 

  1026. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr1</span> <span class="pre">const&amp;)lhs).equal((Dr2</span> <span class="pre">const&amp;)rhs)</span></tt>.</p>
    1027. 

  1027. </dd>
    1028. 

  1028. <dt>Otherwise,</dt>
    1029. 

  1029. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr2</span> <span class="pre">const&amp;)rhs).equal((Dr1</span> <span class="pre">const&amp;)lhs)</span></tt>.</p>
    1030. 

  1030. </dd>
    1031. 

  1031. </dl>
    1032. 

  1032. </td>
    1033. 

  1033. </tr>
    1034. 

  1034. </tbody>
    1035. 

  1035. </table>
    1036. 

  1036. <pre class="literal-block">
    1037. 

  1037. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    1038. 

  1038.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    1039. 

  1039. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    1040. 

  1040. operator !=(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    1041. 

  1041.             iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    1042. 

  1042. </pre>
    1043. 

  1043. <table class="docutils field-list" frame="void" rules="none">
    1044. 

  1044. <col class="field-name" />
    1045. 

  1045. <col class="field-body" />
    1046. 

  1046. <tbody valign="top">
    1047. 

  1047. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">if <tt class="docutils literal"><span class="pre">is_convertible&lt;Dr2,Dr1&gt;::value</span></tt></p>
    1048. 

  1048. <dl class="last docutils">
    1049. 

  1049. <dt>then</dt>
    1050. 

  1050. <dd><p class="first last"><tt class="docutils literal"><span class="pre">!((Dr1</span> <span class="pre">const&amp;)lhs).equal((Dr2</span> <span class="pre">const&amp;)rhs)</span></tt>.</p>
    1051. 

  1051. </dd>
    1052. 

  1052. <dt>Otherwise,</dt>
    1053. 

  1053. <dd><p class="first last"><tt class="docutils literal"><span class="pre">!((Dr2</span> <span class="pre">const&amp;)rhs).equal((Dr1</span> <span class="pre">const&amp;)lhs)</span></tt>.</p>
    1054. 

  1054. </dd>
    1055. 

  1055. </dl>
    1056. 

  1056. </td>
    1057. 

  1057. </tr>
    1058. 

  1058. </tbody>
    1059. 

  1059. </table>
    1060. 

  1060. <pre class="literal-block">
    1061. 

  1061. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    1062. 

  1062.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    1063. 

  1063. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    1064. 

  1064. operator &lt;(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    1065. 

  1065.            iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    1066. 

  1066. </pre>
    1067. 

  1067. <table class="docutils field-list" frame="void" rules="none">
    1068. 

  1068. <col class="field-name" />
    1069. 

  1069. <col class="field-body" />
    1070. 

  1070. <tbody valign="top">
    1071. 

  1071. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">if <tt class="docutils literal"><span class="pre">is_convertible&lt;Dr2,Dr1&gt;::value</span></tt></p>
    1072. 

  1072. <dl class="last docutils">
    1073. 

  1073. <dt>then</dt>
    1074. 

  1074. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr1</span> <span class="pre">const&amp;)lhs).distance_to((Dr2</span> <span class="pre">const&amp;)rhs)</span> <span class="pre">&lt;</span> <span class="pre">0</span></tt>.</p>
    1075. 

  1075. </dd>
    1076. 

  1076. <dt>Otherwise,</dt>
    1077. 

  1077. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr2</span> <span class="pre">const&amp;)rhs).distance_to((Dr1</span> <span class="pre">const&amp;)lhs)</span> <span class="pre">&gt;</span> <span class="pre">0</span></tt>.</p>
    1078. 

  1078. </dd>
    1079. 

  1079. </dl>
    1080. 

  1080. </td>
    1081. 

  1081. </tr>
    1082. 

  1082. </tbody>
    1083. 

  1083. </table>
    1084. 

  1084. <pre class="literal-block">
    1085. 

  1085. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    1086. 

  1086.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    1087. 

  1087. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    1088. 

  1088. operator &lt;=(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    1089. 

  1089.             iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    1090. 

  1090. </pre>
    1091. 

  1091. <table class="docutils field-list" frame="void" rules="none">
    1092. 

  1092. <col class="field-name" />
    1093. 

  1093. <col class="field-body" />
    1094. 

  1094. <tbody valign="top">
    1095. 

  1095. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">if <tt class="docutils literal"><span class="pre">is_convertible&lt;Dr2,Dr1&gt;::value</span></tt></p>
    1096. 

  1096. <dl class="last docutils">
    1097. 

  1097. <dt>then</dt>
    1098. 

  1098. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr1</span> <span class="pre">const&amp;)lhs).distance_to((Dr2</span> <span class="pre">const&amp;)rhs)</span> <span class="pre">&lt;=</span> <span class="pre">0</span></tt>.</p>
    1099. 

  1099. </dd>
    1100. 

  1100. <dt>Otherwise,</dt>
    1101. 

  1101. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr2</span> <span class="pre">const&amp;)rhs).distance_to((Dr1</span> <span class="pre">const&amp;)lhs)</span> <span class="pre">&gt;=</span> <span class="pre">0</span></tt>.</p>
    1102. 

  1102. </dd>
    1103. 

  1103. </dl>
    1104. 

  1104. </td>
    1105. 

  1105. </tr>
    1106. 

  1106. </tbody>
    1107. 

  1107. </table>
    1108. 

  1108. <pre class="literal-block">
    1109. 

  1109. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    1110. 

  1110.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    1111. 

  1111. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    1112. 

  1112. operator &gt;(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    1113. 

  1113.            iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    1114. 

  1114. </pre>
    1115. 

  1115. <table class="docutils field-list" frame="void" rules="none">
    1116. 

  1116. <col class="field-name" />
    1117. 

  1117. <col class="field-body" />
    1118. 

  1118. <tbody valign="top">
    1119. 

  1119. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">if <tt class="docutils literal"><span class="pre">is_convertible&lt;Dr2,Dr1&gt;::value</span></tt></p>
    1120. 

  1120. <dl class="last docutils">
    1121. 

  1121. <dt>then</dt>
    1122. 

  1122. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr1</span> <span class="pre">const&amp;)lhs).distance_to((Dr2</span> <span class="pre">const&amp;)rhs)</span> <span class="pre">&gt;</span> <span class="pre">0</span></tt>.</p>
    1123. 

  1123. </dd>
    1124. 

  1124. <dt>Otherwise,</dt>
    1125. 

  1125. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr2</span> <span class="pre">const&amp;)rhs).distance_to((Dr1</span> <span class="pre">const&amp;)lhs)</span> <span class="pre">&lt;</span> <span class="pre">0</span></tt>.</p>
    1126. 

  1126. </dd>
    1127. 

  1127. </dl>
    1128. 

  1128. </td>
    1129. 

  1129. </tr>
    1130. 

  1130. </tbody>
    1131. 

  1131. </table>
    1132. 

  1132. <pre class="literal-block">
    1133. 

  1133. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    1134. 

  1134.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    1135. 

  1135. typename enable_if_interoperable&lt;Dr1,Dr2,bool&gt;::type
    1136. 

  1136. operator &gt;=(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    1137. 

  1137.             iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    1138. 

  1138. </pre>
    1139. 

  1139. <table class="docutils field-list" frame="void" rules="none">
    1140. 

  1140. <col class="field-name" />
    1141. 

  1141. <col class="field-body" />
    1142. 

  1142. <tbody valign="top">
    1143. 

  1143. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">if <tt class="docutils literal"><span class="pre">is_convertible&lt;Dr2,Dr1&gt;::value</span></tt></p>
    1144. 

  1144. <dl class="last docutils">
    1145. 

  1145. <dt>then</dt>
    1146. 

  1146. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr1</span> <span class="pre">const&amp;)lhs).distance_to((Dr2</span> <span class="pre">const&amp;)rhs)</span> <span class="pre">&gt;=</span> <span class="pre">0</span></tt>.</p>
    1147. 

  1147. </dd>
    1148. 

  1148. <dt>Otherwise,</dt>
    1149. 

  1149. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr2</span> <span class="pre">const&amp;)rhs).distance_to((Dr1</span> <span class="pre">const&amp;)lhs)</span> <span class="pre">&lt;=</span> <span class="pre">0</span></tt>.</p>
    1150. 

  1150. </dd>
    1151. 

  1151. </dl>
    1152. 

  1152. </td>
    1153. 

  1153. </tr>
    1154. 

  1154. </tbody>
    1155. 

  1155. </table>
    1156. 

  1156. <pre class="literal-block" id="minus">
    1157. 

  1157. template &lt;class Dr1, class V1, class TC1, class R1, class D1,
    1158. 

  1158.           class Dr2, class V2, class TC2, class R2, class D2&gt;
    1159. 

  1159. typename enable_if_interoperable&lt;Dr1,Dr2,difference&gt;::type
    1160. 

  1160. operator -(iterator_facade&lt;Dr1,V1,TC1,R1,D1&gt; const&amp; lhs,
    1161. 

  1161.            iterator_facade&lt;Dr2,V2,TC2,R2,D2&gt; const&amp; rhs);
    1162. 

  1162. </pre>
    1163. 

  1163. <table class="docutils field-list" frame="void" rules="none">
    1164. 

  1164. <col class="field-name" />
    1165. 

  1165. <col class="field-body" />
    1166. 

  1166. <tbody valign="top">
    1167. 

  1167. <tr class="field"><th class="field-name">Return Type:</th><td class="field-body"><p class="first">if <tt class="docutils literal"><span class="pre">is_convertible&lt;Dr2,Dr1&gt;::value</span></tt></p>
    1168. 

  1168. <blockquote>
    1169. 

  1169. <dl class="docutils">
    1170. 

  1170. <dt>then</dt>
    1171. 

  1171. <dd><p class="first last"><tt class="docutils literal"><span class="pre">difference</span></tt> shall be
    1172. 

  1172. <tt class="docutils literal"><span class="pre">iterator_traits&lt;Dr1&gt;::difference_type</span></tt>.</p>
    1173. 

  1173. </dd>
    1174. 

  1174. <dt>Otherwise</dt>
    1175. 

  1175. <dd><p class="first last"><tt class="docutils literal"><span class="pre">difference</span></tt> shall be <tt class="docutils literal"><span class="pre">iterator_traits&lt;Dr2&gt;::difference_type</span></tt></p>
    1176. 

  1176. </dd>
    1177. 

  1177. </dl>
    1178. 

  1178. </blockquote>
    1179. 

  1179. </td>
    1180. 

  1180. </tr>
    1181. 

  1181. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">if <tt class="docutils literal"><span class="pre">is_convertible&lt;Dr2,Dr1&gt;::value</span></tt></p>
    1182. 

  1182. <dl class="last docutils">
    1183. 

  1183. <dt>then</dt>
    1184. 

  1184. <dd><p class="first last"><tt class="docutils literal"><span class="pre">-((Dr1</span> <span class="pre">const&amp;)lhs).distance_to((Dr2</span> <span class="pre">const&amp;)rhs)</span></tt>.</p>
    1185. 

  1185. </dd>
    1186. 

  1186. <dt>Otherwise,</dt>
    1187. 

  1187. <dd><p class="first last"><tt class="docutils literal"><span class="pre">((Dr2</span> <span class="pre">const&amp;)rhs).distance_to((Dr1</span> <span class="pre">const&amp;)lhs)</span></tt>.</p>
    1188. 

  1188. </dd>
    1189. 

  1189. </dl>
    1190. 

  1190. </td>
    1191. 

  1191. </tr>
    1192. 

  1192. </tbody>
    1193. 

  1193. </table>
    1194. 

  1194. </div>
    1195. 

  1195. </div>
    1196. 

  1196. <div class="section" id="iterator-adaptor-lib-iterator-adaptor">
    1197. 

  1197. <h2><a class="toc-backref" href="#id33">Iterator adaptor [lib.iterator.adaptor]</a></h2>
    1198. 

  1198. <!-- Distributed under the Boost -->
    1199. 

  1199. <!-- Software License, Version 1.0. (See accompanying -->
    1200. 

  1200. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1201. 

  1201. <!-- Version 1.1 of this ReStructuredText document corresponds to
    1202. 

  1202. n1530_, the paper accepted by the LWG. -->
    1203. 

  1203. <!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. -->
    1204. 

  1204. <p>Each specialization of the <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> class template is derived from
    1205. 

  1205. a specialization of <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>. The core interface functions
    1206. 

  1206. expected by <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> are implemented in terms of the
    1207. 

  1207. <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt>'s <tt class="docutils literal"><span class="pre">Base</span></tt> template parameter. A class derived
    1208. 

  1208. from <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> typically redefines some of the core
    1209. 

  1209. interface functions to adapt the behavior of the <tt class="docutils literal"><span class="pre">Base</span></tt> type.
    1210. 

  1210. Whether the derived class models any of the standard iterator concepts
    1211. 

  1211. depends on the operations supported by the <tt class="docutils literal"><span class="pre">Base</span></tt> type and which
    1212. 

  1212. core interface functions of <tt class="docutils literal"><span class="pre">iterator_facade</span></tt> are redefined in the
    1213. 

  1213. <tt class="docutils literal"><span class="pre">Derived</span></tt> class.</p>
    1214. 

  1214. <div class="section" id="class-template-iterator-adaptor">
    1215. 

  1215. <h3><a class="toc-backref" href="#id34">Class template <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt></a></h3>
    1216. 

  1216. <!-- Distributed under the Boost -->
    1217. 

  1217. <!-- Software License, Version 1.0. (See accompanying -->
    1218. 

  1218. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1219. 

  1219. <!-- Version 1.4 of this ReStructuredText document corresponds to
    1220. 

  1220. n1530_, the paper accepted by the LWG for TR1. -->
    1221. 

  1221. <!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. -->
    1222. 

  1222. <pre class="literal-block">
    1223. 

  1223. template &lt;
    1224. 

  1224.     class Derived
    1225. 

  1225.   , class Base
    1226. 

  1226.   , class Value               = use_default
    1227. 

  1227.   , class CategoryOrTraversal = use_default
    1228. 

  1228.   , class Reference           = use_default
    1229. 

  1229.   , class Difference = use_default
    1230. 

  1230. &gt;
    1231. 

  1231. class iterator_adaptor
    1232. 

  1232.   : public iterator_facade&lt;Derived, <em>V'</em>, <em>C'</em>, <em>R'</em>, <em>D'</em>&gt; // see <a class="reference internal" href="#base-parameters">details</a>
    1233. 

  1233. {
    1234. 

  1234.     friend class iterator_core_access;
    1235. 

  1235.  public:
    1236. 

  1236.     iterator_adaptor();
    1237. 

  1237.     explicit iterator_adaptor(Base const&amp; iter);
    1238. 

  1238.     typedef Base base_type;
    1239. 

  1239.     Base const&amp; base() const;
    1240. 

  1240.  protected:
    1241. 

  1241.     typedef iterator_adaptor iterator_adaptor_;
    1242. 

  1242.     Base const&amp; base_reference() const;
    1243. 

  1243.     Base&amp; base_reference();
    1244. 

  1244.  private: // Core iterator interface for iterator_facade.
    1245. 

  1245.     typename iterator_adaptor::reference dereference() const;
    1246. 

  1246. 

  1247.     template &lt;
    1248. 

  1248.     class OtherDerived, class OtherIterator, class V, class C, class R, class D
    1249. 

  1249.     &gt;
    1250. 

  1250.     bool equal(iterator_adaptor&lt;OtherDerived, OtherIterator, V, C, R, D&gt; const&amp; x) const;
    1251. 

  1251. 

  1252.     void advance(typename iterator_adaptor::difference_type n);
    1253. 

  1253.     void increment();
    1254. 

  1254.     void decrement();
    1255. 

  1255. 

  1256.     template &lt;
    1257. 

  1257.         class OtherDerived, class OtherIterator, class V, class C, class R, class D
    1258. 

  1258.     &gt;
    1259. 

  1259.     typename iterator_adaptor::difference_type distance_to(
    1260. 

  1260.         iterator_adaptor&lt;OtherDerived, OtherIterator, V, C, R, D&gt; const&amp; y) const;
    1261. 

  1261. 

  1262.  private:
    1263. 

  1263.     Base m_iterator; // exposition only
    1264. 

  1264. };
    1265. 

  1265. </pre>
    1266. 

  1266. </div>
    1267. 

  1267. <div class="section" id="iterator-adaptor-requirements">
    1268. 

  1268. <span id="requirements"></span><h3><a class="toc-backref" href="#id35"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> requirements</a></h3>
    1269. 

  1269. <p><tt class="docutils literal"><span class="pre">static_cast&lt;Derived*&gt;(iterator_adaptor*)</span></tt> shall be well-formed.
    1270. 

  1270. The <tt class="docutils literal"><span class="pre">Base</span></tt> argument shall be Assignable and Copy Constructible.</p>
    1271. 

  1271. </div>
    1272. 

  1272. <div class="section" id="iterator-adaptor-base-class-parameters">
    1273. 

  1273. <span id="base-parameters"></span><h3><a class="toc-backref" href="#id36"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> base class parameters</a></h3>
    1274. 

  1274. <p>The <em>V'</em>, <em>C'</em>, <em>R'</em>, and <em>D'</em> parameters of the <tt class="docutils literal"><span class="pre">iterator_facade</span></tt>
    1275. 

  1275. used as a base class in the summary of <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt>
    1276. 

  1276. above are defined as follows:</p>
    1277. 

  1277. <pre class="literal-block">
    1278. 

  1278. <em>V'</em> = if (Value is use_default)
    1279. 

  1279.           return iterator_traits&lt;Base&gt;::value_type
    1280. 

  1280.       else
    1281. 

  1281.           return Value
    1282. 

  1282. 

  1283. <em>C'</em> = if (CategoryOrTraversal is use_default)
    1284. 

  1284.           return iterator_traversal&lt;Base&gt;::type
    1285. 

  1285.       else
    1286. 

  1286.           return CategoryOrTraversal
    1287. 

  1287. 

  1288. <em>R'</em> = if (Reference is use_default)
    1289. 

  1289.           if (Value is use_default)
    1290. 

  1290.               return iterator_traits&lt;Base&gt;::reference
    1291. 

  1291.           else
    1292. 

  1292.               return Value&amp;
    1293. 

  1293.       else
    1294. 

  1294.           return Reference
    1295. 

  1295. 

  1296. <em>D'</em> = if (Difference is use_default)
    1297. 

  1297.           return iterator_traits&lt;Base&gt;::difference_type
    1298. 

  1298.       else
    1299. 

  1299.           return Difference
    1300. 

  1300. </pre>
    1301. 

  1301. <!-- ``iterator_adaptor`` models
    1302. 

  1302. - - - - - - - - - - - - - - - - - - - - - - - - - - -
    1303. 

  1303. 

  1304. In order for ``Derived`` to model the iterator concepts corresponding
    1305. 

  1305. to ``iterator_traits<Derived>::iterator_category``, the expressions
    1306. 

  1306. involving ``m_iterator`` in the specifications of those private member
    1307. 

  1307. functions of ``iterator_adaptor`` that may be called by
    1308. 

  1308. ``iterator_facade<Derived, V, C, R, D>`` in evaluating any valid
    1309. 

  1309. expression involving ``Derived`` in those concepts' requirements. -->
    1310. 

  1310. <!-- The above is confusing and needs a rewrite. -JGS -->
    1311. 

  1311. <!-- That's why it's removed.  We're embracing inheritance, remember? -->
    1312. 

  1312. </div>
    1313. 

  1313. <div class="section" id="iterator-adaptor-public-operations">
    1314. 

  1314. <h3><a class="toc-backref" href="#id37"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> public operations</a></h3>
    1315. 

  1315. <p><tt class="docutils literal"><span class="pre">iterator_adaptor();</span></tt></p>
    1316. 

  1316. <table class="docutils field-list" frame="void" rules="none">
    1317. 

  1317. <col class="field-name" />
    1318. 

  1318. <col class="field-body" />
    1319. 

  1319. <tbody valign="top">
    1320. 

  1320. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">The <tt class="docutils literal"><span class="pre">Base</span></tt> type must be Default Constructible.</td>
    1321. 

  1321. </tr>
    1322. 

  1322. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> with
    1323. 

  1323. <tt class="docutils literal"><span class="pre">m_iterator</span></tt> default constructed.</td>
    1324. 

  1324. </tr>
    1325. 

  1325. </tbody>
    1326. 

  1326. </table>
    1327. 

  1327. <p><tt class="docutils literal"><span class="pre">explicit</span> <span class="pre">iterator_adaptor(Base</span> <span class="pre">const&amp;</span> <span class="pre">iter);</span></tt></p>
    1328. 

  1328. <table class="docutils field-list" frame="void" rules="none">
    1329. 

  1329. <col class="field-name" />
    1330. 

  1330. <col class="field-body" />
    1331. 

  1331. <tbody valign="top">
    1332. 

  1332. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> with
    1333. 

  1333. <tt class="docutils literal"><span class="pre">m_iterator</span></tt> copy constructed from <tt class="docutils literal"><span class="pre">iter</span></tt>.</td>
    1334. 

  1334. </tr>
    1335. 

  1335. </tbody>
    1336. 

  1336. </table>
    1337. 

  1337. <p><tt class="docutils literal"><span class="pre">Base</span> <span class="pre">const&amp;</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
    1338. 

  1338. <table class="docutils field-list" frame="void" rules="none">
    1339. 

  1339. <col class="field-name" />
    1340. 

  1340. <col class="field-body" />
    1341. 

  1341. <tbody valign="top">
    1342. 

  1342. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_iterator</span></tt></td>
    1343. 

  1343. </tr>
    1344. 

  1344. </tbody>
    1345. 

  1345. </table>
    1346. 

  1346. </div>
    1347. 

  1347. <div class="section" id="iterator-adaptor-protected-member-functions">
    1348. 

  1348. <h3><a class="toc-backref" href="#id38"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> protected member functions</a></h3>
    1349. 

  1349. <p><tt class="docutils literal"><span class="pre">Base</span> <span class="pre">const&amp;</span> <span class="pre">base_reference()</span> <span class="pre">const;</span></tt></p>
    1350. 

  1350. <table class="docutils field-list" frame="void" rules="none">
    1351. 

  1351. <col class="field-name" />
    1352. 

  1352. <col class="field-body" />
    1353. 

  1353. <tbody valign="top">
    1354. 

  1354. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">A const reference to <tt class="docutils literal"><span class="pre">m_iterator</span></tt>.</td>
    1355. 

  1355. </tr>
    1356. 

  1356. </tbody>
    1357. 

  1357. </table>
    1358. 

  1358. <p><tt class="docutils literal"><span class="pre">Base&amp;</span> <span class="pre">base_reference();</span></tt></p>
    1359. 

  1359. <table class="docutils field-list" frame="void" rules="none">
    1360. 

  1360. <col class="field-name" />
    1361. 

  1361. <col class="field-body" />
    1362. 

  1362. <tbody valign="top">
    1363. 

  1363. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">A non-const reference to <tt class="docutils literal"><span class="pre">m_iterator</span></tt>.</td>
    1364. 

  1364. </tr>
    1365. 

  1365. </tbody>
    1366. 

  1366. </table>
    1367. 

  1367. </div>
    1368. 

  1368. <div class="section" id="iterator-adaptor-private-member-functions">
    1369. 

  1369. <h3><a class="toc-backref" href="#id39"><tt class="docutils literal"><span class="pre">iterator_adaptor</span></tt> private member functions</a></h3>
    1370. 

  1370. <p><tt class="docutils literal"><span class="pre">typename</span> <span class="pre">iterator_adaptor::reference</span> <span class="pre">dereference()</span> <span class="pre">const;</span></tt></p>
    1371. 

  1371. <table class="docutils field-list" frame="void" rules="none">
    1372. 

  1372. <col class="field-name" />
    1373. 

  1373. <col class="field-body" />
    1374. 

  1374. <tbody valign="top">
    1375. 

  1375. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*m_iterator</span></tt></td>
    1376. 

  1376. </tr>
    1377. 

  1377. </tbody>
    1378. 

  1378. </table>
    1379. 

  1379. <pre class="literal-block">
    1380. 

  1380. template &lt;
    1381. 

  1381. class OtherDerived, class OtherIterator, class V, class C, class R, class D
    1382. 

  1382. &gt;
    1383. 

  1383. bool equal(iterator_adaptor&lt;OtherDerived, OtherIterator, V, C, R, D&gt; const&amp; x) const;
    1384. 

  1384. </pre>
    1385. 

  1385. <table class="docutils field-list" frame="void" rules="none">
    1386. 

  1386. <col class="field-name" />
    1387. 

  1387. <col class="field-body" />
    1388. 

  1388. <tbody valign="top">
    1389. 

  1389. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_iterator</span> <span class="pre">==</span> <span class="pre">x.base()</span></tt></td>
    1390. 

  1390. </tr>
    1391. 

  1391. </tbody>
    1392. 

  1392. </table>
    1393. 

  1393. <p><tt class="docutils literal"><span class="pre">void</span> <span class="pre">advance(typename</span> <span class="pre">iterator_adaptor::difference_type</span> <span class="pre">n);</span></tt></p>
    1394. 

  1394. <table class="docutils field-list" frame="void" rules="none">
    1395. 

  1395. <col class="field-name" />
    1396. 

  1396. <col class="field-body" />
    1397. 

  1397. <tbody valign="top">
    1398. 

  1398. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_iterator</span> <span class="pre">+=</span> <span class="pre">n;</span></tt></td>
    1399. 

  1399. </tr>
    1400. 

  1400. </tbody>
    1401. 

  1401. </table>
    1402. 

  1402. <p><tt class="docutils literal"><span class="pre">void</span> <span class="pre">increment();</span></tt></p>
    1403. 

  1403. <table class="docutils field-list" frame="void" rules="none">
    1404. 

  1404. <col class="field-name" />
    1405. 

  1405. <col class="field-body" />
    1406. 

  1406. <tbody valign="top">
    1407. 

  1407. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">++m_iterator;</span></tt></td>
    1408. 

  1408. </tr>
    1409. 

  1409. </tbody>
    1410. 

  1410. </table>
    1411. 

  1411. <p><tt class="docutils literal"><span class="pre">void</span> <span class="pre">decrement();</span></tt></p>
    1412. 

  1412. <table class="docutils field-list" frame="void" rules="none">
    1413. 

  1413. <col class="field-name" />
    1414. 

  1414. <col class="field-body" />
    1415. 

  1415. <tbody valign="top">
    1416. 

  1416. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">--m_iterator;</span></tt></td>
    1417. 

  1417. </tr>
    1418. 

  1418. </tbody>
    1419. 

  1419. </table>
    1420. 

  1420. <pre class="literal-block">
    1421. 

  1421. template &lt;
    1422. 

  1422.     class OtherDerived, class OtherIterator, class V, class C, class R, class D
    1423. 

  1423. &gt;
    1424. 

  1424. typename iterator_adaptor::difference_type distance_to(
    1425. 

  1425.     iterator_adaptor&lt;OtherDerived, OtherIterator, V, C, R, D&gt; const&amp; y) const;
    1426. 

  1426. </pre>
    1427. 

  1427. <table class="docutils field-list" frame="void" rules="none">
    1428. 

  1428. <col class="field-name" />
    1429. 

  1429. <col class="field-body" />
    1430. 

  1430. <tbody valign="top">
    1431. 

  1431. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">y.base()</span> <span class="pre">-</span> <span class="pre">m_iterator</span></tt></td>
    1432. 

  1432. </tr>
    1433. 

  1433. </tbody>
    1434. 

  1434. </table>
    1435. 

  1435. </div>
    1436. 

  1436. </div>
    1437. 

  1437. <div class="section" id="specialized-adaptors-lib-iterator-special-adaptors">
    1438. 

  1438. <h2><a class="toc-backref" href="#id40">Specialized adaptors [lib.iterator.special.adaptors]</a></h2>
    1439. 

  1439. <p>The <tt class="docutils literal"><span class="pre">enable_if_convertible&lt;X,Y&gt;::type</span></tt> expression used in
    1440. 

  1440. this section is for exposition purposes. The converting constructors
    1441. 

  1441. for specialized adaptors should be only be in an overload set provided
    1442. 

  1442. that an object of type <tt class="docutils literal"><span class="pre">X</span></tt> is implicitly convertible to an object of
    1443. 

  1443. type <tt class="docutils literal"><span class="pre">Y</span></tt>.
    1444. 

  1444. The signatures involving <tt class="docutils literal"><span class="pre">enable_if_convertible</span></tt> should behave
    1445. 

  1445. <em>as-if</em> <tt class="docutils literal"><span class="pre">enable_if_convertible</span></tt> were defined to be:</p>
    1446. 

  1446. <pre class="literal-block">
    1447. 

  1447. template &lt;bool&gt; enable_if_convertible_impl
    1448. 

  1448. {};
    1449. 

  1449. 

  1450. template &lt;&gt; enable_if_convertible_impl&lt;true&gt;
    1451. 

  1451. { struct type; };
    1452. 

  1452. 

  1453. template&lt;typename From, typename To&gt;
    1454. 

  1454. struct enable_if_convertible
    1455. 

  1455.   : enable_if_convertible_impl&lt;is_convertible&lt;From,To&gt;::value&gt;
    1456. 

  1456. {};
    1457. 

  1457. </pre>
    1458. 

  1458. <p>If an expression other than the default argument is used to supply
    1459. 

  1459. the value of a function parameter whose type is written in terms
    1460. 

  1460. of <tt class="docutils literal"><span class="pre">enable_if_convertible</span></tt>, the program is ill-formed, no
    1461. 

  1461. diagnostic required.</p>
    1462. 

  1462. <p>[<em>Note:</em> The <tt class="docutils literal"><span class="pre">enable_if_convertible</span></tt> approach uses SFINAE to
    1463. 

  1463. take the constructor out of the overload set when the types are not
    1464. 

  1464. implicitly convertible.
    1465. 

  1465. ]</p>
    1466. 

  1466. <div class="section" id="indirect-iterator">
    1467. 

  1467. <h3><a class="toc-backref" href="#id41">Indirect iterator</a></h3>
    1468. 

  1468. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    1469. 

  1469. <!-- Software License, Version 1.0. (See accompanying -->
    1470. 

  1470. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1471. 

  1471. <p><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> adapts an iterator by applying an
    1472. 

  1472. <em>extra</em> dereference inside of <tt class="docutils literal"><span class="pre">operator*()</span></tt>. For example, this
    1473. 

  1473. iterator adaptor makes it possible to view a container of pointers
    1474. 

  1474. (e.g. <tt class="docutils literal"><span class="pre">list&lt;foo*&gt;</span></tt>) as if it were a container of the pointed-to type
    1475. 

  1475. (e.g. <tt class="docutils literal"><span class="pre">list&lt;foo&gt;</span></tt>).  <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> depends on two
    1476. 

  1476. auxiliary traits, <tt class="docutils literal"><span class="pre">pointee</span></tt> and <tt class="docutils literal"><span class="pre">indirect_reference</span></tt>, to
    1477. 

  1477. provide support for underlying iterators whose <tt class="docutils literal"><span class="pre">value_type</span></tt> is
    1478. 

  1478. not an iterator.</p>
    1479. 

  1479. <div class="section" id="class-template-pointee">
    1480. 

  1480. <h4><a class="toc-backref" href="#id42">Class template <tt class="docutils literal"><span class="pre">pointee</span></tt></a></h4>
    1481. 

  1481. <!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
    1482. 

  1482. <!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
    1483. 

  1483. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1484. 

  1484. <pre class="literal-block">
    1485. 

  1485. template &lt;class Dereferenceable&gt;
    1486. 

  1486. struct pointee
    1487. 

  1487. {
    1488. 

  1488.     typedef /* see below */ type;
    1489. 

  1489. };
    1490. 

  1490. </pre>
    1491. 

  1491. <table class="docutils field-list" frame="void" rules="none">
    1492. 

  1492. <col class="field-name" />
    1493. 

  1493. <col class="field-body" />
    1494. 

  1494. <tbody valign="top">
    1495. 

  1495. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">For an object <tt class="docutils literal"><span class="pre">x</span></tt> of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>, <tt class="docutils literal"><span class="pre">*x</span></tt>
    1496. 

  1496. is well-formed.  If <tt class="docutils literal"><span class="pre">++x</span></tt> is ill-formed it shall neither be
    1497. 

  1497. ambiguous nor shall it violate access control, and
    1498. 

  1498. <tt class="docutils literal"><span class="pre">Dereferenceable::element_type</span></tt> shall be an accessible type.
    1499. 

  1499. Otherwise <tt class="docutils literal"><span class="pre">iterator_traits&lt;Dereferenceable&gt;::value_type</span></tt> shall
    1500. 

  1500. be well formed.  [Note: These requirements need not apply to
    1501. 

  1501. explicit or partial specializations of <tt class="docutils literal"><span class="pre">pointee</span></tt>]</td>
    1502. 

  1502. </tr>
    1503. 

  1503. </tbody>
    1504. 

  1504. </table>
    1505. 

  1505. <p><tt class="docutils literal"><span class="pre">type</span></tt> is determined according to the following algorithm, where
    1506. 

  1506. <tt class="docutils literal"><span class="pre">x</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>:</p>
    1507. 

  1507. <pre class="literal-block">
    1508. 

  1508. if ( ++x is ill-formed )
    1509. 

  1509. {
    1510. 

  1510.     return ``Dereferenceable::element_type``
    1511. 

  1511. }
    1512. 

  1512. else if (``*x`` is a mutable reference to
    1513. 

  1513.          std::iterator_traits&lt;Dereferenceable&gt;::value_type)
    1514. 

  1514. {
    1515. 

  1515.     return iterator_traits&lt;Dereferenceable&gt;::value_type
    1516. 

  1516. }
    1517. 

  1517. else
    1518. 

  1518. {
    1519. 

  1519.     return iterator_traits&lt;Dereferenceable&gt;::value_type const
    1520. 

  1520. }
    1521. 

  1521. </pre>
    1522. 

  1522. </div>
    1523. 

  1523. <div class="section" id="class-template-indirect-reference">
    1524. 

  1524. <h4><a class="toc-backref" href="#id43">Class template <tt class="docutils literal"><span class="pre">indirect_reference</span></tt></a></h4>
    1525. 

  1525. <!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
    1526. 

  1526. <!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
    1527. 

  1527. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1528. 

  1528. <pre class="literal-block">
    1529. 

  1529. template &lt;class Dereferenceable&gt;
    1530. 

  1530. struct indirect_reference
    1531. 

  1531. {
    1532. 

  1532.     typedef /* see below */ type;
    1533. 

  1533. };
    1534. 

  1534. </pre>
    1535. 

  1535. <table class="docutils field-list" frame="void" rules="none">
    1536. 

  1536. <col class="field-name" />
    1537. 

  1537. <col class="field-body" />
    1538. 

  1538. <tbody valign="top">
    1539. 

  1539. <tr class="field"><th class="field-name">Requires:</th><td class="field-body">For an object <tt class="docutils literal"><span class="pre">x</span></tt> of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>, <tt class="docutils literal"><span class="pre">*x</span></tt>
    1540. 

  1540. is well-formed.  If <tt class="docutils literal"><span class="pre">++x</span></tt> is ill-formed it shall neither be
    1541. 

  1541. ambiguous nor shall it violate access control, and
    1542. 

  1542. <tt class="docutils literal"><span class="pre">pointee&lt;Dereferenceable&gt;::type&amp;</span></tt> shall be well-formed.
    1543. 

  1543. Otherwise <tt class="docutils literal"><span class="pre">iterator_traits&lt;Dereferenceable&gt;::reference</span></tt> shall
    1544. 

  1544. be well formed.  [Note: These requirements need not apply to
    1545. 

  1545. explicit or partial specializations of <tt class="docutils literal"><span class="pre">indirect_reference</span></tt>]</td>
    1546. 

  1546. </tr>
    1547. 

  1547. </tbody>
    1548. 

  1548. </table>
    1549. 

  1549. <p><tt class="docutils literal"><span class="pre">type</span></tt> is determined according to the following algorithm, where
    1550. 

  1550. <tt class="docutils literal"><span class="pre">x</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>:</p>
    1551. 

  1551. <pre class="literal-block">
    1552. 

  1552. if ( ++x is ill-formed )
    1553. 

  1553.     return ``pointee&lt;Dereferenceable&gt;::type&amp;``
    1554. 

  1554. else
    1555. 

  1555.     std::iterator_traits&lt;Dereferenceable&gt;::reference
    1556. 

  1556. </pre>
    1557. 

  1557. </div>
    1558. 

  1558. <div class="section" id="class-template-indirect-iterator">
    1559. 

  1559. <h4><a class="toc-backref" href="#id44">Class template <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt></a></h4>
    1560. 

  1560. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    1561. 

  1561. <!-- Software License, Version 1.0. (See accompanying -->
    1562. 

  1562. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1563. 

  1563. <pre class="literal-block">
    1564. 

  1564. template &lt;
    1565. 

  1565.     class Iterator
    1566. 

  1566.   , class Value = use_default
    1567. 

  1567.   , class CategoryOrTraversal = use_default
    1568. 

  1568.   , class Reference = use_default
    1569. 

  1569.   , class Difference = use_default
    1570. 

  1570. &gt;
    1571. 

  1571. class indirect_iterator
    1572. 

  1572. {
    1573. 

  1573.  public:
    1574. 

  1574.     typedef /* see below */ value_type;
    1575. 

  1575.     typedef /* see below */ reference;
    1576. 

  1576.     typedef /* see below */ pointer;
    1577. 

  1577.     typedef /* see below */ difference_type;
    1578. 

  1578.     typedef /* see below */ iterator_category;
    1579. 

  1579. 

  1580.     indirect_iterator();
    1581. 

  1581.     indirect_iterator(Iterator x);
    1582. 

  1582. 

  1583.     template &lt;
    1584. 

  1584.         class Iterator2, class Value2, class Category2
    1585. 

  1585.       , class Reference2, class Difference2
    1586. 

  1586.     &gt;
    1587. 

  1587.     indirect_iterator(
    1588. 

  1588.         indirect_iterator&lt;
    1589. 

  1589.              Iterator2, Value2, Category2, Reference2, Difference2
    1590. 

  1590.         &gt; const&amp; y
    1591. 

  1591.       , typename enable_if_convertible&lt;Iterator2, Iterator&gt;::type* = 0 // exposition
    1592. 

  1592.     );
    1593. 

  1593. 

  1594.     Iterator const&amp; base() const;
    1595. 

  1595.     reference operator*() const;
    1596. 

  1596.     indirect_iterator&amp; operator++();
    1597. 

  1597.     indirect_iterator&amp; operator--();
    1598. 

  1598. private:
    1599. 

  1599.    Iterator m_iterator; // exposition
    1600. 

  1600. };
    1601. 

  1601. </pre>
    1602. 

  1602. <p>The member types of <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> are defined according to
    1603. 

  1603. the following pseudo-code, where <tt class="docutils literal"><span class="pre">V</span></tt> is
    1604. 

  1604. <tt class="docutils literal"><span class="pre">iterator_traits&lt;Iterator&gt;::value_type</span></tt></p>
    1605. 

  1605. <pre class="literal-block">
    1606. 

  1606. if (Value is use_default) then
    1607. 

  1607.     typedef remove_const&lt;pointee&lt;V&gt;::type&gt;::type value_type;
    1608. 

  1608. else
    1609. 

  1609.     typedef remove_const&lt;Value&gt;::type value_type;
    1610. 

  1610. 

  1611. if (Reference is use_default) then
    1612. 

  1612.     if (Value is use_default) then
    1613. 

  1613.         typedef indirect_reference&lt;V&gt;::type reference;
    1614. 

  1614.     else
    1615. 

  1615.         typedef Value&amp; reference;
    1616. 

  1616. else
    1617. 

  1617.     typedef Reference reference;
    1618. 

  1618. 

  1619. if (Value is use_default) then
    1620. 

  1620.     typedef pointee&lt;V&gt;::type* pointer;
    1621. 

  1621. else
    1622. 

  1622.     typedef Value* pointer;
    1623. 

  1623. 

  1624. if (Difference is use_default)
    1625. 

  1625.     typedef iterator_traits&lt;Iterator&gt;::difference_type difference_type;
    1626. 

  1626. else
    1627. 

  1627.     typedef Difference difference_type;
    1628. 

  1628. 

  1629. if (CategoryOrTraversal is use_default)
    1630. 

  1630.     typedef <em>iterator-category</em> (
    1631. 

  1631.         iterator_traversal&lt;Iterator&gt;::type,``reference``,``value_type``
    1632. 

  1632.     ) iterator_category;
    1633. 

  1633. else
    1634. 

  1634.     typedef <em>iterator-category</em> (
    1635. 

  1635.         CategoryOrTraversal,``reference``,``value_type``
    1636. 

  1636.     ) iterator_category;
    1637. 

  1637. </pre>
    1638. 

  1638. </div>
    1639. 

  1639. <div class="section" id="indirect-iterator-requirements">
    1640. 

  1640. <h4><a class="toc-backref" href="#id45"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> requirements</a></h4>
    1641. 

  1641. <p>The expression <tt class="docutils literal"><span class="pre">*v</span></tt>, where <tt class="docutils literal"><span class="pre">v</span></tt> is an object of
    1642. 

  1642. <tt class="docutils literal"><span class="pre">iterator_traits&lt;Iterator&gt;::value_type</span></tt>, shall be valid
    1643. 

  1643. expression and convertible to <tt class="docutils literal"><span class="pre">reference</span></tt>.  <tt class="docutils literal"><span class="pre">Iterator</span></tt> shall
    1644. 

  1644. model the traversal concept indicated by <tt class="docutils literal"><span class="pre">iterator_category</span></tt>.
    1645. 

  1645. <tt class="docutils literal"><span class="pre">Value</span></tt>, <tt class="docutils literal"><span class="pre">Reference</span></tt>, and <tt class="docutils literal"><span class="pre">Difference</span></tt> shall be chosen so
    1646. 

  1646. that <tt class="docutils literal"><span class="pre">value_type</span></tt>, <tt class="docutils literal"><span class="pre">reference</span></tt>, and <tt class="docutils literal"><span class="pre">difference_type</span></tt> meet
    1647. 

  1647. the requirements indicated by <tt class="docutils literal"><span class="pre">iterator_category</span></tt>.</p>
    1648. 

  1648. <p>[Note: there are further requirements on the
    1649. 

  1649. <tt class="docutils literal"><span class="pre">iterator_traits&lt;Iterator&gt;::value_type</span></tt> if the <tt class="docutils literal"><span class="pre">Value</span></tt>
    1650. 

  1650. parameter is not <tt class="docutils literal"><span class="pre">use_default</span></tt>, as implied by the algorithm for
    1651. 

  1651. deducing the default for the <tt class="docutils literal"><span class="pre">value_type</span></tt> member.]</p>
    1652. 

  1652. </div>
    1653. 

  1653. <div class="section" id="indirect-iterator-models">
    1654. 

  1654. <h4><a class="toc-backref" href="#id46"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> models</a></h4>
    1655. 

  1655. <p>In addition to the concepts indicated by <tt class="docutils literal"><span class="pre">iterator_category</span></tt>
    1656. 

  1656. and by <tt class="docutils literal"><span class="pre">iterator_traversal&lt;indirect_iterator&gt;::type</span></tt>, a
    1657. 

  1657. specialization of <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> models the following
    1658. 

  1658. concepts, Where <tt class="docutils literal"><span class="pre">v</span></tt> is an object of
    1659. 

  1659. <tt class="docutils literal"><span class="pre">iterator_traits&lt;Iterator&gt;::value_type</span></tt>:</p>
    1660. 

  1660. <blockquote>
    1661. 

  1661. <ul class="simple">
    1662. 

  1662. <li>Readable Iterator if <tt class="docutils literal"><span class="pre">reference(*v)</span></tt> is convertible to
    1663. 

  1663. <tt class="docutils literal"><span class="pre">value_type</span></tt>.</li>
    1664. 

  1664. <li>Writable Iterator if <tt class="docutils literal"><span class="pre">reference(*v)</span> <span class="pre">=</span> <span class="pre">t</span></tt> is a valid
    1665. 

  1665. expression (where <tt class="docutils literal"><span class="pre">t</span></tt> is an object of type
    1666. 

  1666. <tt class="docutils literal"><span class="pre">indirect_iterator::value_type</span></tt>)</li>
    1667. 

  1667. <li>Lvalue Iterator if <tt class="docutils literal"><span class="pre">reference</span></tt> is a reference type.</li>
    1668. 

  1668. </ul>
    1669. 

  1669. </blockquote>
    1670. 

  1670. <p><tt class="docutils literal"><span class="pre">indirect_iterator&lt;X,V1,C1,R1,D1&gt;</span></tt> is interoperable with
    1671. 

  1671. <tt class="docutils literal"><span class="pre">indirect_iterator&lt;Y,V2,C2,R2,D2&gt;</span></tt> if and only if <tt class="docutils literal"><span class="pre">X</span></tt> is
    1672. 

  1672. interoperable with <tt class="docutils literal"><span class="pre">Y</span></tt>.</p>
    1673. 

  1673. </div>
    1674. 

  1674. <div class="section" id="indirect-iterator-operations">
    1675. 

  1675. <h4><a class="toc-backref" href="#id47"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> operations</a></h4>
    1676. 

  1676. <p>In addition to the operations required by the concepts described
    1677. 

  1677. above, specializations of <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> provide the
    1678. 

  1678. following operations.</p>
    1679. 

  1679. <p><tt class="docutils literal"><span class="pre">indirect_iterator();</span></tt></p>
    1680. 

  1680. <table class="docutils field-list" frame="void" rules="none">
    1681. 

  1681. <col class="field-name" />
    1682. 

  1682. <col class="field-body" />
    1683. 

  1683. <tbody valign="top">
    1684. 

  1684. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">Iterator</span></tt> must be Default Constructible.</td>
    1685. 

  1685. </tr>
    1686. 

  1686. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs an instance of <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> with
    1687. 

  1687. a default-constructed <tt class="docutils literal"><span class="pre">m_iterator</span></tt>.</td>
    1688. 

  1688. </tr>
    1689. 

  1689. </tbody>
    1690. 

  1690. </table>
    1691. 

  1691. <p><tt class="docutils literal"><span class="pre">indirect_iterator(Iterator</span> <span class="pre">x);</span></tt></p>
    1692. 

  1692. <table class="docutils field-list" frame="void" rules="none">
    1693. 

  1693. <col class="field-name" />
    1694. 

  1694. <col class="field-body" />
    1695. 

  1695. <tbody valign="top">
    1696. 

  1696. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs an instance of <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> with
    1697. 

  1697. <tt class="docutils literal"><span class="pre">m_iterator</span></tt> copy constructed from <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
    1698. 

  1698. </tr>
    1699. 

  1699. </tbody>
    1700. 

  1700. </table>
    1701. 

  1701. <pre class="literal-block">
    1702. 

  1702. template &lt;
    1703. 

  1703.     class Iterator2, class Value2, unsigned Access, class Traversal
    1704. 

  1704.   , class Reference2, class Difference2
    1705. 

  1705. &gt;
    1706. 

  1706. indirect_iterator(
    1707. 

  1707.     indirect_iterator&lt;
    1708. 

  1708.          Iterator2, Value2, Access, Traversal, Reference2, Difference2
    1709. 

  1709.     &gt; const&amp; y
    1710. 

  1710.   , typename enable_if_convertible&lt;Iterator2, Iterator&gt;::type* = 0 // exposition
    1711. 

  1711. );
    1712. 

  1712. </pre>
    1713. 

  1713. <table class="docutils field-list" frame="void" rules="none">
    1714. 

  1714. <col class="field-name" />
    1715. 

  1715. <col class="field-body" />
    1716. 

  1716. <tbody valign="top">
    1717. 

  1717. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">Iterator2</span></tt> is implicitly convertible to <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</td>
    1718. 

  1718. </tr>
    1719. 

  1719. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs an instance of <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> whose
    1720. 

  1720. <tt class="docutils literal"><span class="pre">m_iterator</span></tt> subobject is constructed from <tt class="docutils literal"><span class="pre">y.base()</span></tt>.</td>
    1721. 

  1721. </tr>
    1722. 

  1722. </tbody>
    1723. 

  1723. </table>
    1724. 

  1724. <p><tt class="docutils literal"><span class="pre">Iterator</span> <span class="pre">const&amp;</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
    1725. 

  1725. <table class="docutils field-list" frame="void" rules="none">
    1726. 

  1726. <col class="field-name" />
    1727. 

  1727. <col class="field-body" />
    1728. 

  1728. <tbody valign="top">
    1729. 

  1729. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_iterator</span></tt></td>
    1730. 

  1730. </tr>
    1731. 

  1731. </tbody>
    1732. 

  1732. </table>
    1733. 

  1733. <p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
    1734. 

  1734. <table class="docutils field-list" frame="void" rules="none">
    1735. 

  1735. <col class="field-name" />
    1736. 

  1736. <col class="field-body" />
    1737. 

  1737. <tbody valign="top">
    1738. 

  1738. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">**m_iterator</span></tt></td>
    1739. 

  1739. </tr>
    1740. 

  1740. </tbody>
    1741. 

  1741. </table>
    1742. 

  1742. <p><tt class="docutils literal"><span class="pre">indirect_iterator&amp;</span> <span class="pre">operator++();</span></tt></p>
    1743. 

  1743. <table class="docutils field-list" frame="void" rules="none">
    1744. 

  1744. <col class="field-name" />
    1745. 

  1745. <col class="field-body" />
    1746. 

  1746. <tbody valign="top">
    1747. 

  1747. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">++m_iterator</span></tt></td>
    1748. 

  1748. </tr>
    1749. 

  1749. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    1750. 

  1750. </tr>
    1751. 

  1751. </tbody>
    1752. 

  1752. </table>
    1753. 

  1753. <p><tt class="docutils literal"><span class="pre">indirect_iterator&amp;</span> <span class="pre">operator--();</span></tt></p>
    1754. 

  1754. <table class="docutils field-list" frame="void" rules="none">
    1755. 

  1755. <col class="field-name" />
    1756. 

  1756. <col class="field-body" />
    1757. 

  1757. <tbody valign="top">
    1758. 

  1758. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">--m_iterator</span></tt></td>
    1759. 

  1759. </tr>
    1760. 

  1760. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    1761. 

  1761. </tr>
    1762. 

  1762. </tbody>
    1763. 

  1763. </table>
    1764. 

  1764. </div>
    1765. 

  1765. </div>
    1766. 

  1766. <div class="section" id="reverse-iterator">
    1767. 

  1767. <h3><a class="toc-backref" href="#id48">Reverse iterator</a></h3>
    1768. 

  1768. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    1769. 

  1769. <!-- Software License, Version 1.0. (See accompanying -->
    1770. 

  1770. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1771. 

  1771. <p>The reverse iterator adaptor iterates through the adapted iterator
    1772. 

  1772. range in the opposite direction.</p>
    1773. 

  1773. <div class="section" id="class-template-reverse-iterator">
    1774. 

  1774. <h4><a class="toc-backref" href="#id49">Class template <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt></a></h4>
    1775. 

  1775. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    1776. 

  1776. <!-- Software License, Version 1.0. (See accompanying -->
    1777. 

  1777. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1778. 

  1778. <pre class="literal-block">
    1779. 

  1779. template &lt;class Iterator&gt;
    1780. 

  1780. class reverse_iterator
    1781. 

  1781. {
    1782. 

  1782. public:
    1783. 

  1783.   typedef iterator_traits&lt;Iterator&gt;::value_type value_type;
    1784. 

  1784.   typedef iterator_traits&lt;Iterator&gt;::reference reference;
    1785. 

  1785.   typedef iterator_traits&lt;Iterator&gt;::pointer pointer;
    1786. 

  1786.   typedef iterator_traits&lt;Iterator&gt;::difference_type difference_type;
    1787. 

  1787.   typedef /* see below */ iterator_category;
    1788. 

  1788. 

  1789.   reverse_iterator() {}
    1790. 

  1790.   explicit reverse_iterator(Iterator x) ;
    1791. 

  1791. 

  1792.   template&lt;class OtherIterator&gt;
    1793. 

  1793.   reverse_iterator(
    1794. 

  1794.       reverse_iterator&lt;OtherIterator&gt; const&amp; r
    1795. 

  1795.     , typename enable_if_convertible&lt;OtherIterator, Iterator&gt;::type* = 0 // exposition
    1796. 

  1796.   );
    1797. 

  1797.   Iterator const&amp; base() const;
    1798. 

  1798.   reference operator*() const;
    1799. 

  1799.   reverse_iterator&amp; operator++();
    1800. 

  1800.   reverse_iterator&amp; operator--();
    1801. 

  1801. private:
    1802. 

  1802.   Iterator m_iterator; // exposition
    1803. 

  1803. };
    1804. 

  1804. </pre>
    1805. 

  1805. <p>If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Random Access Traversal Iterator and Readable
    1806. 

  1806. Lvalue Iterator, then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
    1807. 

  1807. <tt class="docutils literal"><span class="pre">random_access_iterator_tag</span></tt>. Otherwise, if
    1808. 

  1808. <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Bidirectional Traversal Iterator and Readable
    1809. 

  1809. Lvalue Iterator, then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
    1810. 

  1810. <tt class="docutils literal"><span class="pre">bidirectional_iterator_tag</span></tt>. Otherwise, <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
    1811. 

  1811. convertible to <tt class="docutils literal"><span class="pre">input_iterator_tag</span></tt>.</p>
    1812. 

  1812. </div>
    1813. 

  1813. <div class="section" id="reverse-iterator-requirements">
    1814. 

  1814. <h4><a class="toc-backref" href="#id50"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> requirements</a></h4>
    1815. 

  1815. <p><tt class="docutils literal"><span class="pre">Iterator</span></tt> must be a model of Bidirectional Traversal Iterator.  The
    1816. 

  1816. type <tt class="docutils literal"><span class="pre">iterator_traits&lt;Iterator&gt;::reference</span></tt> must be the type of
    1817. 

  1817. <tt class="docutils literal"><span class="pre">*i</span></tt>, where <tt class="docutils literal"><span class="pre">i</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</p>
    1818. 

  1818. </div>
    1819. 

  1819. <div class="section" id="reverse-iterator-models">
    1820. 

  1820. <h4><a class="toc-backref" href="#id51"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> models</a></h4>
    1821. 

  1821. <p>A specialization of <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> models the same iterator
    1822. 

  1822. traversal and iterator access concepts modeled by its <tt class="docutils literal"><span class="pre">Iterator</span></tt>
    1823. 

  1823. argument.  In addition, it may model old iterator concepts
    1824. 

  1824. specified in the following table:</p>
    1825. 

  1825. <table border="1" class="docutils">
    1826. 

  1826. <colgroup>
    1827. 

  1827. <col width="53%" />
    1828. 

  1828. <col width="47%" />
    1829. 

  1829. </colgroup>
    1830. 

  1830. <thead valign="bottom">
    1831. 

  1831. <tr><th class="head">If <tt class="docutils literal"><span class="pre">I</span></tt> models</th>
    1832. 

  1832. <th class="head">then <tt class="docutils literal"><span class="pre">reverse_iterator&lt;I&gt;</span></tt> models</th>
    1833. 

  1833. </tr>
    1834. 

  1834. </thead>
    1835. 

  1835. <tbody valign="top">
    1836. 

  1836. <tr><td>Readable Lvalue Iterator,
    1837. 

  1837. Bidirectional Traversal Iterator</td>
    1838. 

  1838. <td>Bidirectional Iterator</td>
    1839. 

  1839. </tr>
    1840. 

  1840. <tr><td>Writable Lvalue Iterator,
    1841. 

  1841. Bidirectional Traversal Iterator</td>
    1842. 

  1842. <td>Mutable Bidirectional Iterator</td>
    1843. 

  1843. </tr>
    1844. 

  1844. <tr><td>Readable Lvalue Iterator,
    1845. 

  1845. Random Access Traversal Iterator</td>
    1846. 

  1846. <td>Random Access Iterator</td>
    1847. 

  1847. </tr>
    1848. 

  1848. <tr><td>Writable Lvalue Iterator,
    1849. 

  1849. Random Access Traversal Iterator</td>
    1850. 

  1850. <td>Mutable Random Access Iterator</td>
    1851. 

  1851. </tr>
    1852. 

  1852. </tbody>
    1853. 

  1853. </table>
    1854. 

  1854. <p><tt class="docutils literal"><span class="pre">reverse_iterator&lt;X&gt;</span></tt> is interoperable with
    1855. 

  1855. <tt class="docutils literal"><span class="pre">reverse_iterator&lt;Y&gt;</span></tt> if and only if <tt class="docutils literal"><span class="pre">X</span></tt> is interoperable with
    1856. 

  1856. <tt class="docutils literal"><span class="pre">Y</span></tt>.</p>
    1857. 

  1857. </div>
    1858. 

  1858. <div class="section" id="reverse-iterator-operations">
    1859. 

  1859. <h4><a class="toc-backref" href="#id52"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> operations</a></h4>
    1860. 

  1860. <p>In addition to the operations required by the concepts modeled by
    1861. 

  1861. <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt>, <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> provides the following
    1862. 

  1862. operations.</p>
    1863. 

  1863. <p><tt class="docutils literal"><span class="pre">reverse_iterator();</span></tt></p>
    1864. 

  1864. <table class="docutils field-list" frame="void" rules="none">
    1865. 

  1865. <col class="field-name" />
    1866. 

  1866. <col class="field-body" />
    1867. 

  1867. <tbody valign="top">
    1868. 

  1868. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">Iterator</span></tt> must be Default Constructible.</td>
    1869. 

  1869. </tr>
    1870. 

  1870. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs an instance of <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_iterator</span></tt>
    1871. 

  1871. default constructed.</td>
    1872. 

  1872. </tr>
    1873. 

  1873. </tbody>
    1874. 

  1874. </table>
    1875. 

  1875. <p><tt class="docutils literal"><span class="pre">explicit</span> <span class="pre">reverse_iterator(Iterator</span> <span class="pre">x);</span></tt></p>
    1876. 

  1876. <table class="docutils field-list" frame="void" rules="none">
    1877. 

  1877. <col class="field-name" />
    1878. 

  1878. <col class="field-body" />
    1879. 

  1879. <tbody valign="top">
    1880. 

  1880. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs an instance of <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> with
    1881. 

  1881. <tt class="docutils literal"><span class="pre">m_iterator</span></tt> copy constructed from <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
    1882. 

  1882. </tr>
    1883. 

  1883. </tbody>
    1884. 

  1884. </table>
    1885. 

  1885. <pre class="literal-block">
    1886. 

  1886. template&lt;class OtherIterator&gt;
    1887. 

  1887. reverse_iterator(
    1888. 

  1888.     reverse_iterator&lt;OtherIterator&gt; const&amp; r
    1889. 

  1889.   , typename enable_if_convertible&lt;OtherIterator, Iterator&gt;::type* = 0 // exposition
    1890. 

  1890. );
    1891. 

  1891. </pre>
    1892. 

  1892. <table class="docutils field-list" frame="void" rules="none">
    1893. 

  1893. <col class="field-name" />
    1894. 

  1894. <col class="field-body" />
    1895. 

  1895. <tbody valign="top">
    1896. 

  1896. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">OtherIterator</span></tt> is implicitly convertible to <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</td>
    1897. 

  1897. </tr>
    1898. 

  1898. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs instance of <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> whose
    1899. 

  1899. <tt class="docutils literal"><span class="pre">m_iterator</span></tt> subobject is constructed from <tt class="docutils literal"><span class="pre">y.base()</span></tt>.</td>
    1900. 

  1900. </tr>
    1901. 

  1901. </tbody>
    1902. 

  1902. </table>
    1903. 

  1903. <p><tt class="docutils literal"><span class="pre">Iterator</span> <span class="pre">const&amp;</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
    1904. 

  1904. <table class="docutils field-list" frame="void" rules="none">
    1905. 

  1905. <col class="field-name" />
    1906. 

  1906. <col class="field-body" />
    1907. 

  1907. <tbody valign="top">
    1908. 

  1908. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_iterator</span></tt></td>
    1909. 

  1909. </tr>
    1910. 

  1910. </tbody>
    1911. 

  1911. </table>
    1912. 

  1912. <p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
    1913. 

  1913. <table class="docutils field-list" frame="void" rules="none">
    1914. 

  1914. <col class="field-name" />
    1915. 

  1915. <col class="field-body" />
    1916. 

  1916. <tbody valign="top">
    1917. 

  1917. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"></td>
    1918. 

  1918. </tr>
    1919. 

  1919. </tbody>
    1920. 

  1920. </table>
    1921. 

  1921. <pre class="literal-block">
    1922. 

  1922. Iterator tmp = m_iterator;
    1923. 

  1923. return *--tmp;
    1924. 

  1924. </pre>
    1925. 

  1925. <p><tt class="docutils literal"><span class="pre">reverse_iterator&amp;</span> <span class="pre">operator++();</span></tt></p>
    1926. 

  1926. <table class="docutils field-list" frame="void" rules="none">
    1927. 

  1927. <col class="field-name" />
    1928. 

  1928. <col class="field-body" />
    1929. 

  1929. <tbody valign="top">
    1930. 

  1930. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">--m_iterator</span></tt></td>
    1931. 

  1931. </tr>
    1932. 

  1932. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    1933. 

  1933. </tr>
    1934. 

  1934. </tbody>
    1935. 

  1935. </table>
    1936. 

  1936. <p><tt class="docutils literal"><span class="pre">reverse_iterator&amp;</span> <span class="pre">operator--();</span></tt></p>
    1937. 

  1937. <table class="docutils field-list" frame="void" rules="none">
    1938. 

  1938. <col class="field-name" />
    1939. 

  1939. <col class="field-body" />
    1940. 

  1940. <tbody valign="top">
    1941. 

  1941. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">++m_iterator</span></tt></td>
    1942. 

  1942. </tr>
    1943. 

  1943. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    1944. 

  1944. </tr>
    1945. 

  1945. </tbody>
    1946. 

  1946. </table>
    1947. 

  1947. </div>
    1948. 

  1948. </div>
    1949. 

  1949. <div class="section" id="transform-iterator">
    1950. 

  1950. <h3><a class="toc-backref" href="#id53">Transform iterator</a></h3>
    1951. 

  1951. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    1952. 

  1952. <!-- Software License, Version 1.0. (See accompanying -->
    1953. 

  1953. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1954. 

  1954. <p>The transform iterator adapts an iterator by modifying the
    1955. 

  1955. <tt class="docutils literal"><span class="pre">operator*</span></tt> to apply a function object to the result of
    1956. 

  1956. dereferencing the iterator and returning the result.</p>
    1957. 

  1957. <div class="section" id="class-template-transform-iterator">
    1958. 

  1958. <h4><a class="toc-backref" href="#id54">Class template <tt class="docutils literal"><span class="pre">transform_iterator</span></tt></a></h4>
    1959. 

  1959. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    1960. 

  1960. <!-- Software License, Version 1.0. (See accompanying -->
    1961. 

  1961. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    1962. 

  1962. <!-- Version 1.3 of this document was accepted for TR1 -->
    1963. 

  1963. <pre class="literal-block">
    1964. 

  1964. template &lt;class UnaryFunction,
    1965. 

  1965.           class Iterator,
    1966. 

  1966.           class Reference = use_default,
    1967. 

  1967.           class Value = use_default&gt;
    1968. 

  1968. class transform_iterator
    1969. 

  1969. {
    1970. 

  1970. public:
    1971. 

  1971.   typedef /* see below */ value_type;
    1972. 

  1972.   typedef /* see below */ reference;
    1973. 

  1973.   typedef /* see below */ pointer;
    1974. 

  1974.   typedef iterator_traits&lt;Iterator&gt;::difference_type difference_type;
    1975. 

  1975.   typedef /* see below */ iterator_category;
    1976. 

  1976. 

  1977.   transform_iterator();
    1978. 

  1978.   transform_iterator(Iterator const&amp; x, UnaryFunction f);
    1979. 

  1979. 

  1980.   template&lt;class F2, class I2, class R2, class V2&gt;
    1981. 

  1981.   transform_iterator(
    1982. 

  1982.         transform_iterator&lt;F2, I2, R2, V2&gt; const&amp; t
    1983. 

  1983.       , typename enable_if_convertible&lt;I2, Iterator&gt;::type* = 0      // exposition only
    1984. 

  1984.       , typename enable_if_convertible&lt;F2, UnaryFunction&gt;::type* = 0 // exposition only
    1985. 

  1985.   );
    1986. 

  1986.   UnaryFunction functor() const;
    1987. 

  1987.   Iterator const&amp; base() const;
    1988. 

  1988.   reference operator*() const;
    1989. 

  1989.   transform_iterator&amp; operator++();
    1990. 

  1990.   transform_iterator&amp; operator--();
    1991. 

  1991. private:
    1992. 

  1992.   Iterator m_iterator; // exposition only
    1993. 

  1993.   UnaryFunction m_f;   // exposition only
    1994. 

  1994. };
    1995. 

  1995. </pre>
    1996. 

  1996. <p>If <tt class="docutils literal"><span class="pre">Reference</span></tt> is <tt class="docutils literal"><span class="pre">use_default</span></tt> then the <tt class="docutils literal"><span class="pre">reference</span></tt> member of
    1997. 

  1997. <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> is
    1998. 

  1998. <tt class="docutils literal"><span class="pre">result_of&lt;UnaryFunction(iterator_traits&lt;Iterator&gt;::reference)&gt;::type</span></tt>.
    1999. 

  1999. Otherwise, <tt class="docutils literal"><span class="pre">reference</span></tt> is <tt class="docutils literal"><span class="pre">Reference</span></tt>.</p>
    2000. 

  2000. <p>If <tt class="docutils literal"><span class="pre">Value</span></tt> is <tt class="docutils literal"><span class="pre">use_default</span></tt> then the <tt class="docutils literal"><span class="pre">value_type</span></tt> member is
    2001. 

  2001. <tt class="docutils literal"><span class="pre">remove_cv&lt;remove_reference&lt;reference&gt;</span> <span class="pre">&gt;::type</span></tt>.  Otherwise,
    2002. 

  2002. <tt class="docutils literal"><span class="pre">value_type</span></tt> is <tt class="docutils literal"><span class="pre">Value</span></tt>.</p>
    2003. 

  2003. <p>If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Readable Lvalue Iterator and if <tt class="docutils literal"><span class="pre">Iterator</span></tt>
    2004. 

  2004. models Random Access Traversal Iterator, then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
    2005. 

  2005. convertible to <tt class="docutils literal"><span class="pre">random_access_iterator_tag</span></tt>. Otherwise, if
    2006. 

  2006. <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Bidirectional Traversal Iterator, then
    2007. 

  2007. <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
    2008. 

  2008. <tt class="docutils literal"><span class="pre">bidirectional_iterator_tag</span></tt>.  Otherwise <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
    2009. 

  2009. convertible to <tt class="docutils literal"><span class="pre">forward_iterator_tag</span></tt>. If <tt class="docutils literal"><span class="pre">Iterator</span></tt> does not
    2010. 

  2010. model Readable Lvalue Iterator then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
    2011. 

  2011. convertible to <tt class="docutils literal"><span class="pre">input_iterator_tag</span></tt>.</p>
    2012. 

  2012. </div>
    2013. 

  2013. <div class="section" id="transform-iterator-requirements">
    2014. 

  2014. <h4><a class="toc-backref" href="#id55"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> requirements</a></h4>
    2015. 

  2015. <p>The type <tt class="docutils literal"><span class="pre">UnaryFunction</span></tt> must be Assignable, Copy Constructible, and
    2016. 

  2016. the expression <tt class="docutils literal"><span class="pre">f(*i)</span></tt> must be valid where <tt class="docutils literal"><span class="pre">f</span></tt> is an object of
    2017. 

  2017. type <tt class="docutils literal"><span class="pre">UnaryFunction</span></tt>, <tt class="docutils literal"><span class="pre">i</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Iterator</span></tt>, and
    2018. 

  2018. where the type of <tt class="docutils literal"><span class="pre">f(*i)</span></tt> must be
    2019. 

  2019. <tt class="docutils literal"><span class="pre">result_of&lt;UnaryFunction(iterator_traits&lt;Iterator&gt;::reference)&gt;::type</span></tt>.</p>
    2020. 

  2020. <p>The argument <tt class="docutils literal"><span class="pre">Iterator</span></tt> shall model Readable Iterator.</p>
    2021. 

  2021. </div>
    2022. 

  2022. <div class="section" id="transform-iterator-models">
    2023. 

  2023. <h4><a class="toc-backref" href="#id56"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models</a></h4>
    2024. 

  2024. <p>The resulting <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models the most refined of the
    2025. 

  2025. following that is also modeled by <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</p>
    2026. 

  2026. <blockquote>
    2027. 

  2027. <ul class="simple">
    2028. 

  2028. <li>Writable Lvalue Iterator if <tt class="docutils literal"><span class="pre">transform_iterator::reference</span></tt> is a non-const reference.</li>
    2029. 

  2029. <li>Readable Lvalue Iterator if <tt class="docutils literal"><span class="pre">transform_iterator::reference</span></tt> is a const reference.</li>
    2030. 

  2030. <li>Readable Iterator otherwise.</li>
    2031. 

  2031. </ul>
    2032. 

  2032. </blockquote>
    2033. 

  2033. <p>The <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models the most refined standard traversal
    2034. 

  2034. concept that is modeled by the <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument.</p>
    2035. 

  2035. <p>If <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> is a model of Readable Lvalue Iterator then
    2036. 

  2036. it models the following original iterator concepts depending on what
    2037. 

  2037. the <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument models.</p>
    2038. 

  2038. <table border="1" class="docutils">
    2039. 

  2039. <colgroup>
    2040. 

  2040. <col width="47%" />
    2041. 

  2041. <col width="53%" />
    2042. 

  2042. </colgroup>
    2043. 

  2043. <thead valign="bottom">
    2044. 

  2044. <tr><th class="head">If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models</th>
    2045. 

  2045. <th class="head">then <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models</th>
    2046. 

  2046. </tr>
    2047. 

  2047. </thead>
    2048. 

  2048. <tbody valign="top">
    2049. 

  2049. <tr><td>Single Pass Iterator</td>
    2050. 

  2050. <td>Input Iterator</td>
    2051. 

  2051. </tr>
    2052. 

  2052. <tr><td>Forward Traversal Iterator</td>
    2053. 

  2053. <td>Forward Iterator</td>
    2054. 

  2054. </tr>
    2055. 

  2055. <tr><td>Bidirectional Traversal Iterator</td>
    2056. 

  2056. <td>Bidirectional Iterator</td>
    2057. 

  2057. </tr>
    2058. 

  2058. <tr><td>Random Access Traversal Iterator</td>
    2059. 

  2059. <td>Random Access Iterator</td>
    2060. 

  2060. </tr>
    2061. 

  2061. </tbody>
    2062. 

  2062. </table>
    2063. 

  2063. <p>If <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> models Writable Lvalue Iterator then it is a
    2064. 

  2064. mutable iterator (as defined in the old iterator requirements).</p>
    2065. 

  2065. <p><tt class="docutils literal"><span class="pre">transform_iterator&lt;F1,</span> <span class="pre">X,</span> <span class="pre">R1,</span> <span class="pre">V1&gt;</span></tt> is interoperable with
    2066. 

  2066. <tt class="docutils literal"><span class="pre">transform_iterator&lt;F2,</span> <span class="pre">Y,</span> <span class="pre">R2,</span> <span class="pre">V2&gt;</span></tt> if and only if <tt class="docutils literal"><span class="pre">X</span></tt> is
    2067. 

  2067. interoperable with <tt class="docutils literal"><span class="pre">Y</span></tt>.</p>
    2068. 

  2068. </div>
    2069. 

  2069. <div class="section" id="transform-iterator-operations">
    2070. 

  2070. <h4><a class="toc-backref" href="#id57"><tt class="docutils literal"><span class="pre">transform_iterator</span></tt> operations</a></h4>
    2071. 

  2071. <p>In addition to the operations required by the concepts modeled by
    2072. 

  2072. <tt class="docutils literal"><span class="pre">transform_iterator</span></tt>, <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> provides the following
    2073. 

  2073. operations.</p>
    2074. 

  2074. <p><tt class="docutils literal"><span class="pre">transform_iterator();</span></tt></p>
    2075. 

  2075. <table class="docutils field-list" frame="void" rules="none">
    2076. 

  2076. <col class="field-name" />
    2077. 

  2077. <col class="field-body" />
    2078. 

  2078. <tbody valign="top">
    2079. 

  2079. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_f</span></tt>
    2080. 

  2080. and <tt class="docutils literal"><span class="pre">m_iterator</span></tt> default constructed.</td>
    2081. 

  2081. </tr>
    2082. 

  2082. </tbody>
    2083. 

  2083. </table>
    2084. 

  2084. <p><tt class="docutils literal"><span class="pre">transform_iterator(Iterator</span> <span class="pre">const&amp;</span> <span class="pre">x,</span> <span class="pre">UnaryFunction</span> <span class="pre">f);</span></tt></p>
    2085. 

  2085. <table class="docutils field-list" frame="void" rules="none">
    2086. 

  2086. <col class="field-name" />
    2087. 

  2087. <col class="field-body" />
    2088. 

  2088. <tbody valign="top">
    2089. 

  2089. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_f</span></tt>
    2090. 

  2090. initialized to <tt class="docutils literal"><span class="pre">f</span></tt> and <tt class="docutils literal"><span class="pre">m_iterator</span></tt> initialized to <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
    2091. 

  2091. </tr>
    2092. 

  2092. </tbody>
    2093. 

  2093. </table>
    2094. 

  2094. <pre class="literal-block">
    2095. 

  2095. template&lt;class F2, class I2, class R2, class V2&gt;
    2096. 

  2096. transform_iterator(
    2097. 

  2097.       transform_iterator&lt;F2, I2, R2, V2&gt; const&amp; t
    2098. 

  2098.     , typename enable_if_convertible&lt;I2, Iterator&gt;::type* = 0      // exposition only
    2099. 

  2099.     , typename enable_if_convertible&lt;F2, UnaryFunction&gt;::type* = 0 // exposition only
    2100. 

  2100. );
    2101. 

  2101. </pre>
    2102. 

  2102. <table class="docutils field-list" frame="void" rules="none">
    2103. 

  2103. <col class="field-name" />
    2104. 

  2104. <col class="field-body" />
    2105. 

  2105. <tbody valign="top">
    2106. 

  2106. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">transform_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_f</span></tt>
    2107. 

  2107. initialized to <tt class="docutils literal"><span class="pre">t.functor()</span></tt> and <tt class="docutils literal"><span class="pre">m_iterator</span></tt> initialized to
    2108. 

  2108. <tt class="docutils literal"><span class="pre">t.base()</span></tt>.</td>
    2109. 

  2109. </tr>
    2110. 

  2110. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">OtherIterator</span></tt> is implicitly convertible to <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</td>
    2111. 

  2111. </tr>
    2112. 

  2112. </tbody>
    2113. 

  2113. </table>
    2114. 

  2114. <p><tt class="docutils literal"><span class="pre">UnaryFunction</span> <span class="pre">functor()</span> <span class="pre">const;</span></tt></p>
    2115. 

  2115. <table class="docutils field-list" frame="void" rules="none">
    2116. 

  2116. <col class="field-name" />
    2117. 

  2117. <col class="field-body" />
    2118. 

  2118. <tbody valign="top">
    2119. 

  2119. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_f</span></tt></td>
    2120. 

  2120. </tr>
    2121. 

  2121. </tbody>
    2122. 

  2122. </table>
    2123. 

  2123. <p><tt class="docutils literal"><span class="pre">Iterator</span> <span class="pre">const&amp;</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
    2124. 

  2124. <table class="docutils field-list" frame="void" rules="none">
    2125. 

  2125. <col class="field-name" />
    2126. 

  2126. <col class="field-body" />
    2127. 

  2127. <tbody valign="top">
    2128. 

  2128. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_iterator</span></tt></td>
    2129. 

  2129. </tr>
    2130. 

  2130. </tbody>
    2131. 

  2131. </table>
    2132. 

  2132. <p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
    2133. 

  2133. <table class="docutils field-list" frame="void" rules="none">
    2134. 

  2134. <col class="field-name" />
    2135. 

  2135. <col class="field-body" />
    2136. 

  2136. <tbody valign="top">
    2137. 

  2137. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_f(*m_iterator)</span></tt></td>
    2138. 

  2138. </tr>
    2139. 

  2139. </tbody>
    2140. 

  2140. </table>
    2141. 

  2141. <p><tt class="docutils literal"><span class="pre">transform_iterator&amp;</span> <span class="pre">operator++();</span></tt></p>
    2142. 

  2142. <table class="docutils field-list" frame="void" rules="none">
    2143. 

  2143. <col class="field-name" />
    2144. 

  2144. <col class="field-body" />
    2145. 

  2145. <tbody valign="top">
    2146. 

  2146. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">++m_iterator</span></tt></td>
    2147. 

  2147. </tr>
    2148. 

  2148. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    2149. 

  2149. </tr>
    2150. 

  2150. </tbody>
    2151. 

  2151. </table>
    2152. 

  2152. <p><tt class="docutils literal"><span class="pre">transform_iterator&amp;</span> <span class="pre">operator--();</span></tt></p>
    2153. 

  2153. <table class="docutils field-list" frame="void" rules="none">
    2154. 

  2154. <col class="field-name" />
    2155. 

  2155. <col class="field-body" />
    2156. 

  2156. <tbody valign="top">
    2157. 

  2157. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">--m_iterator</span></tt></td>
    2158. 

  2158. </tr>
    2159. 

  2159. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    2160. 

  2160. </tr>
    2161. 

  2161. </tbody>
    2162. 

  2162. </table>
    2163. 

  2163. </div>
    2164. 

  2164. </div>
    2165. 

  2165. <div class="section" id="filter-iterator">
    2166. 

  2166. <h3><a class="toc-backref" href="#id58">Filter iterator</a></h3>
    2167. 

  2167. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    2168. 

  2168. <!-- Software License, Version 1.0. (See accompanying -->
    2169. 

  2169. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    2170. 

  2170. <p>The filter iterator adaptor creates a view of an iterator range in
    2171. 

  2171. which some elements of the range are skipped. A predicate function
    2172. 

  2172. object controls which elements are skipped. When the predicate is
    2173. 

  2173. applied to an element, if it returns <tt class="docutils literal"><span class="pre">true</span></tt> then the element is
    2174. 

  2174. retained and if it returns <tt class="docutils literal"><span class="pre">false</span></tt> then the element is skipped
    2175. 

  2175. over. When skipping over elements, it is necessary for the filter
    2176. 

  2176. adaptor to know when to stop so as to avoid going past the end of the
    2177. 

  2177. underlying range. A filter iterator is therefore constructed with pair
    2178. 

  2178. of iterators indicating the range of elements in the unfiltered
    2179. 

  2179. sequence to be traversed.</p>
    2180. 

  2180. <div class="section" id="class-template-filter-iterator">
    2181. 

  2181. <h4><a class="toc-backref" href="#id59">Class template <tt class="docutils literal"><span class="pre">filter_iterator</span></tt></a></h4>
    2182. 

  2182. <!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt -->
    2183. 

  2183. <!-- 2004. Use, modification and distribution is subject to the Boost -->
    2184. 

  2184. <!-- Software License, Version 1.0. (See accompanying  file -->
    2185. 

  2185. <!-- LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    2186. 

  2186. <pre class="literal-block">
    2187. 

  2187. template &lt;class Predicate, class Iterator&gt;
    2188. 

  2188. class filter_iterator
    2189. 

  2189. {
    2190. 

  2190.  public:
    2191. 

  2191.     typedef iterator_traits&lt;Iterator&gt;::value_type value_type;
    2192. 

  2192.     typedef iterator_traits&lt;Iterator&gt;::reference reference;
    2193. 

  2193.     typedef iterator_traits&lt;Iterator&gt;::pointer pointer;
    2194. 

  2194.     typedef iterator_traits&lt;Iterator&gt;::difference_type difference_type;
    2195. 

  2195.     typedef /* see below */ iterator_category;
    2196. 

  2196. 

  2197.     filter_iterator();
    2198. 

  2198.     filter_iterator(Predicate f, Iterator x, Iterator end = Iterator());
    2199. 

  2199.     filter_iterator(Iterator x, Iterator end = Iterator());
    2200. 

  2200.     template&lt;class OtherIterator&gt;
    2201. 

  2201.     filter_iterator(
    2202. 

  2202.         filter_iterator&lt;Predicate, OtherIterator&gt; const&amp; t
    2203. 

  2203.         , typename enable_if_convertible&lt;OtherIterator, Iterator&gt;::type* = 0 // exposition
    2204. 

  2204.         );
    2205. 

  2205.     Predicate predicate() const;
    2206. 

  2206.     Iterator end() const;
    2207. 

  2207.     Iterator const&amp; base() const;
    2208. 

  2208.     reference operator*() const;
    2209. 

  2209.     filter_iterator&amp; operator++();
    2210. 

  2210. private:
    2211. 

  2211.     Predicate m_pred; // exposition only
    2212. 

  2212.     Iterator m_iter;  // exposition only
    2213. 

  2213.     Iterator m_end;   // exposition only
    2214. 

  2214. };
    2215. 

  2215. </pre>
    2216. 

  2216. <p>If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Readable Lvalue Iterator and Bidirectional Traversal
    2217. 

  2217. Iterator then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
    2218. 

  2218. <tt class="docutils literal"><span class="pre">std::bidirectional_iterator_tag</span></tt>.
    2219. 

  2219. Otherwise, if <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Readable Lvalue Iterator and Forward Traversal
    2220. 

  2220. Iterator then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
    2221. 

  2221. <tt class="docutils literal"><span class="pre">std::forward_iterator_tag</span></tt>.
    2222. 

  2222. Otherwise <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
    2223. 

  2223. convertible to <tt class="docutils literal"><span class="pre">std::input_iterator_tag</span></tt>.</p>
    2224. 

  2224. </div>
    2225. 

  2225. <div class="section" id="filter-iterator-requirements">
    2226. 

  2226. <h4><a class="toc-backref" href="#id60"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> requirements</a></h4>
    2227. 

  2227. <p>The <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument shall meet the requirements of Readable
    2228. 

  2228. Iterator and Single Pass Iterator or it shall meet the requirements of
    2229. 

  2229. Input Iterator.</p>
    2230. 

  2230. <p>The <tt class="docutils literal"><span class="pre">Predicate</span></tt> argument must be Assignable, Copy Constructible, and
    2231. 

  2231. the expression <tt class="docutils literal"><span class="pre">p(x)</span></tt> must be valid where <tt class="docutils literal"><span class="pre">p</span></tt> is an object of type
    2232. 

  2232. <tt class="docutils literal"><span class="pre">Predicate</span></tt>, <tt class="docutils literal"><span class="pre">x</span></tt> is an object of type
    2233. 

  2233. <tt class="docutils literal"><span class="pre">iterator_traits&lt;Iterator&gt;::value_type</span></tt>, and where the type of
    2234. 

  2234. <tt class="docutils literal"><span class="pre">p(x)</span></tt> must be convertible to <tt class="docutils literal"><span class="pre">bool</span></tt>.</p>
    2235. 

  2235. </div>
    2236. 

  2236. <div class="section" id="filter-iterator-models">
    2237. 

  2237. <h4><a class="toc-backref" href="#id61"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</a></h4>
    2238. 

  2238. <p>The concepts that <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models are dependent on which
    2239. 

  2239. concepts the <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument models, as specified in the
    2240. 

  2240. following tables.</p>
    2241. 

  2241. <table border="1" class="docutils">
    2242. 

  2242. <colgroup>
    2243. 

  2243. <col width="44%" />
    2244. 

  2244. <col width="56%" />
    2245. 

  2245. </colgroup>
    2246. 

  2246. <thead valign="bottom">
    2247. 

  2247. <tr><th class="head">If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models</th>
    2248. 

  2248. <th class="head">then <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</th>
    2249. 

  2249. </tr>
    2250. 

  2250. </thead>
    2251. 

  2251. <tbody valign="top">
    2252. 

  2252. <tr><td>Single Pass Iterator</td>
    2253. 

  2253. <td>Single Pass Iterator</td>
    2254. 

  2254. </tr>
    2255. 

  2255. <tr><td>Forward Traversal Iterator</td>
    2256. 

  2256. <td>Forward Traversal Iterator</td>
    2257. 

  2257. </tr>
    2258. 

  2258. <tr><td>Bidirectional Traversal Iterator</td>
    2259. 

  2259. <td>Bidirectional Traversal Iterator</td>
    2260. 

  2260. </tr>
    2261. 

  2261. </tbody>
    2262. 

  2262. </table>
    2263. 

  2263. <table border="1" class="docutils">
    2264. 

  2264. <colgroup>
    2265. 

  2265. <col width="41%" />
    2266. 

  2266. <col width="59%" />
    2267. 

  2267. </colgroup>
    2268. 

  2268. <thead valign="bottom">
    2269. 

  2269. <tr><th class="head">If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models</th>
    2270. 

  2270. <th class="head">then <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</th>
    2271. 

  2271. </tr>
    2272. 

  2272. </thead>
    2273. 

  2273. <tbody valign="top">
    2274. 

  2274. <tr><td>Readable Iterator</td>
    2275. 

  2275. <td>Readable Iterator</td>
    2276. 

  2276. </tr>
    2277. 

  2277. <tr><td>Writable Iterator</td>
    2278. 

  2278. <td>Writable Iterator</td>
    2279. 

  2279. </tr>
    2280. 

  2280. <tr><td>Lvalue Iterator</td>
    2281. 

  2281. <td>Lvalue Iterator</td>
    2282. 

  2282. </tr>
    2283. 

  2283. </tbody>
    2284. 

  2284. </table>
    2285. 

  2285. <table border="1" class="docutils">
    2286. 

  2286. <colgroup>
    2287. 

  2287. <col width="63%" />
    2288. 

  2288. <col width="38%" />
    2289. 

  2289. </colgroup>
    2290. 

  2290. <thead valign="bottom">
    2291. 

  2291. <tr><th class="head">If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models</th>
    2292. 

  2292. <th class="head">then <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</th>
    2293. 

  2293. </tr>
    2294. 

  2294. </thead>
    2295. 

  2295. <tbody valign="top">
    2296. 

  2296. <tr><td>Readable Iterator, Single Pass Iterator</td>
    2297. 

  2297. <td>Input Iterator</td>
    2298. 

  2298. </tr>
    2299. 

  2299. <tr><td>Readable Lvalue Iterator, Forward Traversal Iterator</td>
    2300. 

  2300. <td>Forward Iterator</td>
    2301. 

  2301. </tr>
    2302. 

  2302. <tr><td>Writable Lvalue Iterator, Forward Traversal Iterator</td>
    2303. 

  2303. <td>Mutable Forward Iterator</td>
    2304. 

  2304. </tr>
    2305. 

  2305. <tr><td>Writable Lvalue Iterator, Bidirectional Iterator</td>
    2306. 

  2306. <td>Mutable Bidirectional Iterator</td>
    2307. 

  2307. </tr>
    2308. 

  2308. </tbody>
    2309. 

  2309. </table>
    2310. 

  2310. <p><tt class="docutils literal"><span class="pre">filter_iterator&lt;P1,</span> <span class="pre">X&gt;</span></tt> is interoperable with <tt class="docutils literal"><span class="pre">filter_iterator&lt;P2,</span> <span class="pre">Y&gt;</span></tt>
    2311. 

  2311. if and only if <tt class="docutils literal"><span class="pre">X</span></tt> is interoperable with <tt class="docutils literal"><span class="pre">Y</span></tt>.</p>
    2312. 

  2312. </div>
    2313. 

  2313. <div class="section" id="filter-iterator-operations">
    2314. 

  2314. <h4><a class="toc-backref" href="#id62"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> operations</a></h4>
    2315. 

  2315. <p>In addition to those operations required by the concepts that
    2316. 

  2316. <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models, <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> provides the following
    2317. 

  2317. operations.</p>
    2318. 

  2318. <p><tt class="docutils literal"><span class="pre">filter_iterator();</span></tt></p>
    2319. 

  2319. <table class="docutils field-list" frame="void" rules="none">
    2320. 

  2320. <col class="field-name" />
    2321. 

  2321. <col class="field-body" />
    2322. 

  2322. <tbody valign="top">
    2323. 

  2323. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">Predicate</span></tt> and <tt class="docutils literal"><span class="pre">Iterator</span></tt> must be Default Constructible.</td>
    2324. 

  2324. </tr>
    2325. 

  2325. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs a <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> whose``m_pred``,  <tt class="docutils literal"><span class="pre">m_iter</span></tt>, and <tt class="docutils literal"><span class="pre">m_end</span></tt>
    2326. 

  2326. members are a default constructed.</td>
    2327. 

  2327. </tr>
    2328. 

  2328. </tbody>
    2329. 

  2329. </table>
    2330. 

  2330. <p><tt class="docutils literal"><span class="pre">filter_iterator(Predicate</span> <span class="pre">f,</span> <span class="pre">Iterator</span> <span class="pre">x,</span> <span class="pre">Iterator</span> <span class="pre">end</span> <span class="pre">=</span> <span class="pre">Iterator());</span></tt></p>
    2331. 

  2331. <table class="docutils field-list" frame="void" rules="none">
    2332. 

  2332. <col class="field-name" />
    2333. 

  2333. <col class="field-body" />
    2334. 

  2334. <tbody valign="top">
    2335. 

  2335. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs a <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> where <tt class="docutils literal"><span class="pre">m_iter</span></tt> is either
    2336. 

  2336. the first position in the range <tt class="docutils literal"><span class="pre">[x,end)</span></tt> such that <tt class="docutils literal"><span class="pre">f(*m_iter)</span> <span class="pre">==</span> <span class="pre">true</span></tt>
    2337. 

  2337. or else``m_iter == end``. The member <tt class="docutils literal"><span class="pre">m_pred</span></tt> is constructed from
    2338. 

  2338. <tt class="docutils literal"><span class="pre">f</span></tt> and <tt class="docutils literal"><span class="pre">m_end</span></tt> from <tt class="docutils literal"><span class="pre">end</span></tt>.</td>
    2339. 

  2339. </tr>
    2340. 

  2340. </tbody>
    2341. 

  2341. </table>
    2342. 

  2342. <p><tt class="docutils literal"><span class="pre">filter_iterator(Iterator</span> <span class="pre">x,</span> <span class="pre">Iterator</span> <span class="pre">end</span> <span class="pre">=</span> <span class="pre">Iterator());</span></tt></p>
    2343. 

  2343. <table class="docutils field-list" frame="void" rules="none">
    2344. 

  2344. <col class="field-name" />
    2345. 

  2345. <col class="field-body" />
    2346. 

  2346. <tbody valign="top">
    2347. 

  2347. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">Predicate</span></tt> must be Default Constructible and
    2348. 

  2348. <tt class="docutils literal"><span class="pre">Predicate</span></tt> is a class type (not a function pointer).</td>
    2349. 

  2349. </tr>
    2350. 

  2350. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs a <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> where <tt class="docutils literal"><span class="pre">m_iter</span></tt> is either
    2351. 

  2351. the first position in the range <tt class="docutils literal"><span class="pre">[x,end)</span></tt> such that <tt class="docutils literal"><span class="pre">m_pred(*m_iter)</span> <span class="pre">==</span> <span class="pre">true</span></tt>
    2352. 

  2352. or else``m_iter == end``. The member <tt class="docutils literal"><span class="pre">m_pred</span></tt> is default constructed.</td>
    2353. 

  2353. </tr>
    2354. 

  2354. </tbody>
    2355. 

  2355. </table>
    2356. 

  2356. <pre class="literal-block">
    2357. 

  2357. template &lt;class OtherIterator&gt;
    2358. 

  2358. filter_iterator(
    2359. 

  2359.     filter_iterator&lt;Predicate, OtherIterator&gt; const&amp; t
    2360. 

  2360.     , typename enable_if_convertible&lt;OtherIterator, Iterator&gt;::type* = 0 // exposition
    2361. 

  2361.     );``
    2362. 

  2362. </pre>
    2363. 

  2363. <table class="docutils field-list" frame="void" rules="none">
    2364. 

  2364. <col class="field-name" />
    2365. 

  2365. <col class="field-body" />
    2366. 

  2366. <tbody valign="top">
    2367. 

  2367. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">OtherIterator</span></tt> is implicitly convertible to <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</td>
    2368. 

  2368. </tr>
    2369. 

  2369. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs a filter iterator whose members are copied from <tt class="docutils literal"><span class="pre">t</span></tt>.</td>
    2370. 

  2370. </tr>
    2371. 

  2371. </tbody>
    2372. 

  2372. </table>
    2373. 

  2373. <p><tt class="docutils literal"><span class="pre">Predicate</span> <span class="pre">predicate()</span> <span class="pre">const;</span></tt></p>
    2374. 

  2374. <table class="docutils field-list" frame="void" rules="none">
    2375. 

  2375. <col class="field-name" />
    2376. 

  2376. <col class="field-body" />
    2377. 

  2377. <tbody valign="top">
    2378. 

  2378. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_pred</span></tt></td>
    2379. 

  2379. </tr>
    2380. 

  2380. </tbody>
    2381. 

  2381. </table>
    2382. 

  2382. <p><tt class="docutils literal"><span class="pre">Iterator</span> <span class="pre">end()</span> <span class="pre">const;</span></tt></p>
    2383. 

  2383. <table class="docutils field-list" frame="void" rules="none">
    2384. 

  2384. <col class="field-name" />
    2385. 

  2385. <col class="field-body" />
    2386. 

  2386. <tbody valign="top">
    2387. 

  2387. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_end</span></tt></td>
    2388. 

  2388. </tr>
    2389. 

  2389. </tbody>
    2390. 

  2390. </table>
    2391. 

  2391. <p><tt class="docutils literal"><span class="pre">Iterator</span> <span class="pre">const&amp;</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
    2392. 

  2392. <table class="docutils field-list" frame="void" rules="none">
    2393. 

  2393. <col class="field-name" />
    2394. 

  2394. <col class="field-body" />
    2395. 

  2395. <tbody valign="top">
    2396. 

  2396. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_iterator</span></tt></td>
    2397. 

  2397. </tr>
    2398. 

  2398. </tbody>
    2399. 

  2399. </table>
    2400. 

  2400. <p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
    2401. 

  2401. <table class="docutils field-list" frame="void" rules="none">
    2402. 

  2402. <col class="field-name" />
    2403. 

  2403. <col class="field-body" />
    2404. 

  2404. <tbody valign="top">
    2405. 

  2405. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*m_iter</span></tt></td>
    2406. 

  2406. </tr>
    2407. 

  2407. </tbody>
    2408. 

  2408. </table>
    2409. 

  2409. <p><tt class="docutils literal"><span class="pre">filter_iterator&amp;</span> <span class="pre">operator++();</span></tt></p>
    2410. 

  2410. <table class="docutils field-list" frame="void" rules="none">
    2411. 

  2411. <col class="field-name" />
    2412. 

  2412. <col class="field-body" />
    2413. 

  2413. <tbody valign="top">
    2414. 

  2414. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Increments <tt class="docutils literal"><span class="pre">m_iter</span></tt> and then continues to
    2415. 

  2415. increment <tt class="docutils literal"><span class="pre">m_iter</span></tt> until either <tt class="docutils literal"><span class="pre">m_iter</span> <span class="pre">==</span> <span class="pre">m_end</span></tt>
    2416. 

  2416. or <tt class="docutils literal"><span class="pre">m_pred(*m_iter)</span> <span class="pre">==</span> <span class="pre">true</span></tt>.</td>
    2417. 

  2417. </tr>
    2418. 

  2418. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    2419. 

  2419. </tr>
    2420. 

  2420. </tbody>
    2421. 

  2421. </table>
    2422. 

  2422. </div>
    2423. 

  2423. </div>
    2424. 

  2424. <div class="section" id="counting-iterator">
    2425. 

  2425. <h3><a class="toc-backref" href="#id63">Counting iterator</a></h3>
    2426. 

  2426. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    2427. 

  2427. <!-- Software License, Version 1.0. (See accompanying -->
    2428. 

  2428. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    2429. 

  2429. <p><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> adapts an object by adding an <tt class="docutils literal"><span class="pre">operator*</span></tt> that
    2430. 

  2430. returns the current value of the object. All other iterator operations
    2431. 

  2431. are forwarded to the adapted object.</p>
    2432. 

  2432. <div class="section" id="class-template-counting-iterator">
    2433. 

  2433. <h4><a class="toc-backref" href="#id64">Class template <tt class="docutils literal"><span class="pre">counting_iterator</span></tt></a></h4>
    2434. 

  2434. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    2435. 

  2435. <!-- Software License, Version 1.0. (See accompanying -->
    2436. 

  2436. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    2437. 

  2437. <pre class="literal-block">
    2438. 

  2438. template &lt;
    2439. 

  2439.     class Incrementable
    2440. 

  2440.   , class CategoryOrTraversal = use_default
    2441. 

  2441.   , class Difference = use_default
    2442. 

  2442. &gt;
    2443. 

  2443. class counting_iterator
    2444. 

  2444. {
    2445. 

  2445. public:
    2446. 

  2446.     typedef Incrementable value_type;
    2447. 

  2447.     typedef const Incrementable&amp; reference;
    2448. 

  2448.     typedef const Incrementable* pointer;
    2449. 

  2449.     typedef /* see below */ difference_type;
    2450. 

  2450.     typedef /* see below */ iterator_category;
    2451. 

  2451. 

  2452.     counting_iterator();
    2453. 

  2453.     counting_iterator(counting_iterator const&amp; rhs);
    2454. 

  2454.     explicit counting_iterator(Incrementable x);
    2455. 

  2455.     Incrementable const&amp; base() const;
    2456. 

  2456.     reference operator*() const;
    2457. 

  2457.     counting_iterator&amp; operator++();
    2458. 

  2458.     counting_iterator&amp; operator--();
    2459. 

  2459. private:
    2460. 

  2460.     Incrementable m_inc; // exposition
    2461. 

  2461. };
    2462. 

  2462. </pre>
    2463. 

  2463. <p>If the <tt class="docutils literal"><span class="pre">Difference</span></tt> argument is <tt class="docutils literal"><span class="pre">use_default</span></tt> then
    2464. 

  2464. <tt class="docutils literal"><span class="pre">difference_type</span></tt> is an unspecified signed integral
    2465. 

  2465. type. Otherwise <tt class="docutils literal"><span class="pre">difference_type</span></tt> is <tt class="docutils literal"><span class="pre">Difference</span></tt>.</p>
    2466. 

  2466. <p><tt class="docutils literal"><span class="pre">iterator_category</span></tt> is determined according to the following
    2467. 

  2467. algorithm:</p>
    2468. 

  2468. <pre class="literal-block">
    2469. 

  2469. if (CategoryOrTraversal is not use_default)
    2470. 

  2470.     return CategoryOrTraversal
    2471. 

  2471. else if (numeric_limits&lt;Incrementable&gt;::is_specialized)
    2472. 

  2472.     return <a class="reference internal" href="#id12"><em>iterator-category</em></a>(
    2473. 

  2473.         random_access_traversal_tag, Incrementable, const Incrementable&amp;)
    2474. 

  2474. else
    2475. 

  2475.     return <a class="reference internal" href="#id12"><em>iterator-category</em></a>(
    2476. 

  2476.          iterator_traversal&lt;Incrementable&gt;::type,
    2477. 

  2477.          Incrementable, const Incrementable&amp;)
    2478. 

  2478. </pre>
    2479. 

  2479. <dl class="docutils">
    2480. 

  2480. <dt>[<em>Note:</em> implementers are encouraged to provide an implementation of</dt>
    2481. 

  2481. <dd><tt class="docutils literal"><span class="pre">operator-</span></tt> and a <tt class="docutils literal"><span class="pre">difference_type</span></tt> that avoids overflows in
    2482. 

  2482. the cases where <tt class="docutils literal"><span class="pre">std::numeric_limits&lt;Incrementable&gt;::is_specialized</span></tt>
    2483. 

  2483. is true.]</dd>
    2484. 

  2484. </dl>
    2485. 

  2485. </div>
    2486. 

  2486. <div class="section" id="counting-iterator-requirements">
    2487. 

  2487. <h4><a class="toc-backref" href="#id65"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> requirements</a></h4>
    2488. 

  2488. <p>The <tt class="docutils literal"><span class="pre">Incrementable</span></tt> argument shall be Copy Constructible and Assignable.</p>
    2489. 

  2489. <p>If <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to <tt class="docutils literal"><span class="pre">forward_iterator_tag</span></tt>
    2490. 

  2490. or <tt class="docutils literal"><span class="pre">forward_traversal_tag</span></tt>, the following must be well-formed:</p>
    2491. 

  2491. <pre class="literal-block">
    2492. 

  2492. Incrementable i, j;
    2493. 

  2493. ++i;         // pre-increment
    2494. 

  2494. i == j;      // operator equal
    2495. 

  2495. </pre>
    2496. 

  2496. <p>If <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
    2497. 

  2497. <tt class="docutils literal"><span class="pre">bidirectional_iterator_tag</span></tt> or <tt class="docutils literal"><span class="pre">bidirectional_traversal_tag</span></tt>,
    2498. 

  2498. the following expression must also be well-formed:</p>
    2499. 

  2499. <pre class="literal-block">
    2500. 

  2500. --i
    2501. 

  2501. </pre>
    2502. 

  2502. <p>If <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
    2503. 

  2503. <tt class="docutils literal"><span class="pre">random_access_iterator_tag</span></tt> or <tt class="docutils literal"><span class="pre">random_access_traversal_tag</span></tt>,
    2504. 

  2504. the following must must also be valid:</p>
    2505. 

  2505. <pre class="literal-block">
    2506. 

  2506. counting_iterator::difference_type n;
    2507. 

  2507. i += n;
    2508. 

  2508. n = i - j;
    2509. 

  2509. i &lt; j;
    2510. 

  2510. </pre>
    2511. 

  2511. </div>
    2512. 

  2512. <div class="section" id="counting-iterator-models">
    2513. 

  2513. <h4><a class="toc-backref" href="#id66"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models</a></h4>
    2514. 

  2514. <p>Specializations of <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> model Readable Lvalue
    2515. 

  2515. Iterator. In addition, they model the concepts corresponding to the
    2516. 

  2516. iterator tags to which their <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible.
    2517. 

  2517. Also, if <tt class="docutils literal"><span class="pre">CategoryOrTraversal</span></tt> is not <tt class="docutils literal"><span class="pre">use_default</span></tt> then
    2518. 

  2518. <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models the concept corresponding to the iterator
    2519. 

  2519. tag <tt class="docutils literal"><span class="pre">CategoryOrTraversal</span></tt>.  Otherwise, if
    2520. 

  2520. <tt class="docutils literal"><span class="pre">numeric_limits&lt;Incrementable&gt;::is_specialized</span></tt>, then
    2521. 

  2521. <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models Random Access Traversal Iterator.
    2522. 

  2522. Otherwise, <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models the same iterator traversal
    2523. 

  2523. concepts modeled by <tt class="docutils literal"><span class="pre">Incrementable</span></tt>.</p>
    2524. 

  2524. <p><tt class="docutils literal"><span class="pre">counting_iterator&lt;X,C1,D1&gt;</span></tt> is interoperable with
    2525. 

  2525. <tt class="docutils literal"><span class="pre">counting_iterator&lt;Y,C2,D2&gt;</span></tt> if and only if <tt class="docutils literal"><span class="pre">X</span></tt> is
    2526. 

  2526. interoperable with <tt class="docutils literal"><span class="pre">Y</span></tt>.</p>
    2527. 

  2527. </div>
    2528. 

  2528. <div class="section" id="counting-iterator-operations">
    2529. 

  2529. <h4><a class="toc-backref" href="#id67"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> operations</a></h4>
    2530. 

  2530. <p>In addition to the operations required by the concepts modeled by
    2531. 

  2531. <tt class="docutils literal"><span class="pre">counting_iterator</span></tt>, <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> provides the following
    2532. 

  2532. operations.</p>
    2533. 

  2533. <p><tt class="docutils literal"><span class="pre">counting_iterator();</span></tt></p>
    2534. 

  2534. <table class="docutils field-list" frame="void" rules="none">
    2535. 

  2535. <col class="field-name" />
    2536. 

  2536. <col class="field-body" />
    2537. 

  2537. <tbody valign="top">
    2538. 

  2538. <tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">Incrementable</span></tt> is Default Constructible.</td>
    2539. 

  2539. </tr>
    2540. 

  2540. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Default construct the member <tt class="docutils literal"><span class="pre">m_inc</span></tt>.</td>
    2541. 

  2541. </tr>
    2542. 

  2542. </tbody>
    2543. 

  2543. </table>
    2544. 

  2544. <p><tt class="docutils literal"><span class="pre">counting_iterator(counting_iterator</span> <span class="pre">const&amp;</span> <span class="pre">rhs);</span></tt></p>
    2545. 

  2545. <table class="docutils field-list" frame="void" rules="none">
    2546. 

  2546. <col class="field-name" />
    2547. 

  2547. <col class="field-body" />
    2548. 

  2548. <tbody valign="top">
    2549. 

  2549. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Construct member <tt class="docutils literal"><span class="pre">m_inc</span></tt> from <tt class="docutils literal"><span class="pre">rhs.m_inc</span></tt>.</td>
    2550. 

  2550. </tr>
    2551. 

  2551. </tbody>
    2552. 

  2552. </table>
    2553. 

  2553. <p><tt class="docutils literal"><span class="pre">explicit</span> <span class="pre">counting_iterator(Incrementable</span> <span class="pre">x);</span></tt></p>
    2554. 

  2554. <table class="docutils field-list" frame="void" rules="none">
    2555. 

  2555. <col class="field-name" />
    2556. 

  2556. <col class="field-body" />
    2557. 

  2557. <tbody valign="top">
    2558. 

  2558. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Construct member <tt class="docutils literal"><span class="pre">m_inc</span></tt> from <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
    2559. 

  2559. </tr>
    2560. 

  2560. </tbody>
    2561. 

  2561. </table>
    2562. 

  2562. <p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
    2563. 

  2563. <table class="docutils field-list" frame="void" rules="none">
    2564. 

  2564. <col class="field-name" />
    2565. 

  2565. <col class="field-body" />
    2566. 

  2566. <tbody valign="top">
    2567. 

  2567. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_inc</span></tt></td>
    2568. 

  2568. </tr>
    2569. 

  2569. </tbody>
    2570. 

  2570. </table>
    2571. 

  2571. <p><tt class="docutils literal"><span class="pre">counting_iterator&amp;</span> <span class="pre">operator++();</span></tt></p>
    2572. 

  2572. <table class="docutils field-list" frame="void" rules="none">
    2573. 

  2573. <col class="field-name" />
    2574. 

  2574. <col class="field-body" />
    2575. 

  2575. <tbody valign="top">
    2576. 

  2576. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">++m_inc</span></tt></td>
    2577. 

  2577. </tr>
    2578. 

  2578. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    2579. 

  2579. </tr>
    2580. 

  2580. </tbody>
    2581. 

  2581. </table>
    2582. 

  2582. <p><tt class="docutils literal"><span class="pre">counting_iterator&amp;</span> <span class="pre">operator--();</span></tt></p>
    2583. 

  2583. <table class="docutils field-list" frame="void" rules="none">
    2584. 

  2584. <col class="field-name" />
    2585. 

  2585. <col class="field-body" />
    2586. 

  2586. <tbody valign="top">
    2587. 

  2587. <tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">--m_inc</span></tt></td>
    2588. 

  2588. </tr>
    2589. 

  2589. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    2590. 

  2590. </tr>
    2591. 

  2591. </tbody>
    2592. 

  2592. </table>
    2593. 

  2593. <p><tt class="docutils literal"><span class="pre">Incrementable</span> <span class="pre">const&amp;</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
    2594. 

  2594. <table class="docutils field-list" frame="void" rules="none">
    2595. 

  2595. <col class="field-name" />
    2596. 

  2596. <col class="field-body" />
    2597. 

  2597. <tbody valign="top">
    2598. 

  2598. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_inc</span></tt></td>
    2599. 

  2599. </tr>
    2600. 

  2600. </tbody>
    2601. 

  2601. </table>
    2602. 

  2602. </div>
    2603. 

  2603. </div>
    2604. 

  2604. <div class="section" id="function-output-iterator">
    2605. 

  2605. <h3><a class="toc-backref" href="#id68">Function output iterator</a></h3>
    2606. 

  2606. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    2607. 

  2607. <!-- Software License, Version 1.0. (See accompanying -->
    2608. 

  2608. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    2609. 

  2609. <p>The function output iterator adaptor makes it easier to create custom
    2610. 

  2610. output iterators. The adaptor takes a unary function and creates a
    2611. 

  2611. model of Output Iterator. Each item assigned to the output iterator is
    2612. 

  2612. passed as an argument to the unary function.  The motivation for this
    2613. 

  2613. iterator is that creating a conforming output iterator is non-trivial,
    2614. 

  2614. particularly because the proper implementation usually requires a
    2615. 

  2615. proxy object.</p>
    2616. 

  2616. <div class="section" id="class-template-function-output-iterator">
    2617. 

  2617. <h4><a class="toc-backref" href="#id69">Class template <tt class="docutils literal"><span class="pre">function_output_iterator</span></tt></a></h4>
    2618. 

  2618. <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
    2619. 

  2619. <!-- Software License, Version 1.0. (See accompanying -->
    2620. 

  2620. <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
    2621. 

  2621. </div>
    2622. 

  2622. <div class="section" id="header">
    2623. 

  2623. <h4><a class="toc-backref" href="#id70">Header</a></h4>
    2624. 

  2624. <pre class="literal-block">
    2625. 

  2625. #include &lt;boost/function_output_iterator.hpp&gt;
    2626. 

  2626. </pre>
    2627. 

  2627. <pre class="literal-block">
    2628. 

  2628. template &lt;class UnaryFunction&gt;
    2629. 

  2629. class function_output_iterator {
    2630. 

  2630. public:
    2631. 

  2631.   typedef std::output_iterator_tag iterator_category;
    2632. 

  2632.   typedef void                     value_type;
    2633. 

  2633.   typedef void                     difference_type;
    2634. 

  2634.   typedef void                     pointer;
    2635. 

  2635.   typedef void                     reference;
    2636. 

  2636. 

  2637.   explicit function_output_iterator();
    2638. 

  2638. 

  2639.   explicit function_output_iterator(const UnaryFunction&amp; f);
    2640. 

  2640. 

  2641.   /* see below */ operator*();
    2642. 

  2642.   function_output_iterator&amp; operator++();
    2643. 

  2643.   function_output_iterator&amp; operator++(int);
    2644. 

  2644. private:
    2645. 

  2645.   UnaryFunction m_f;     // exposition only
    2646. 

  2646. };
    2647. 

  2647. </pre>
    2648. 

  2648. </div>
    2649. 

  2649. <div class="section" id="function-output-iterator-requirements">
    2650. 

  2650. <h4><a class="toc-backref" href="#id71"><tt class="docutils literal"><span class="pre">function_output_iterator</span></tt> requirements</a></h4>
    2651. 

  2651. <p><tt class="docutils literal"><span class="pre">UnaryFunction</span></tt> must be Assignable and Copy Constructible.</p>
    2652. 

  2652. </div>
    2653. 

  2653. <div class="section" id="function-output-iterator-models">
    2654. 

  2654. <h4><a class="toc-backref" href="#id72"><tt class="docutils literal"><span class="pre">function_output_iterator</span></tt> models</a></h4>
    2655. 

  2655. <p><tt class="docutils literal"><span class="pre">function_output_iterator</span></tt> is a model of the Writable and
    2656. 

  2656. Incrementable Iterator concepts.</p>
    2657. 

  2657. </div>
    2658. 

  2658. <div class="section" id="function-output-iterator-operations">
    2659. 

  2659. <h4><a class="toc-backref" href="#id73"><tt class="docutils literal"><span class="pre">function_output_iterator</span></tt> operations</a></h4>
    2660. 

  2660. <p><tt class="docutils literal"><span class="pre">explicit</span> <span class="pre">function_output_iterator(const</span> <span class="pre">UnaryFunction&amp;</span> <span class="pre">f</span> <span class="pre">=</span> <span class="pre">UnaryFunction());</span></tt></p>
    2661. 

  2661. <table class="docutils field-list" frame="void" rules="none">
    2662. 

  2662. <col class="field-name" />
    2663. 

  2663. <col class="field-body" />
    2664. 

  2664. <tbody valign="top">
    2665. 

  2665. <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs an instance of <tt class="docutils literal"><span class="pre">function_output_iterator</span></tt>
    2666. 

  2666. with <tt class="docutils literal"><span class="pre">m_f</span></tt> constructed from <tt class="docutils literal"><span class="pre">f</span></tt>.</td>
    2667. 

  2667. </tr>
    2668. 

  2668. </tbody>
    2669. 

  2669. </table>
    2670. 

  2670. <p><tt class="docutils literal"><span class="pre">operator*();</span></tt></p>
    2671. 

  2671. <table class="docutils field-list" frame="void" rules="none">
    2672. 

  2672. <col class="field-name" />
    2673. 

  2673. <col class="field-body" />
    2674. 

  2674. <tbody valign="top">
    2675. 

  2675. <tr class="field"><th class="field-name">Returns:</th><td class="field-body">An object <tt class="docutils literal"><span class="pre">r</span></tt> of unspecified type such that <tt class="docutils literal"><span class="pre">r</span> <span class="pre">=</span> <span class="pre">t</span></tt>
    2676. 

  2676. is equivalent to <tt class="docutils literal"><span class="pre">m_f(t)</span></tt> for all <tt class="docutils literal"><span class="pre">t</span></tt>.</td>
    2677. 

  2677. </tr>
    2678. 

  2678. </tbody>
    2679. 

  2679. </table>
    2680. 

  2680. <p><tt class="docutils literal"><span class="pre">function_output_iterator&amp;</span> <span class="pre">operator++();</span></tt></p>
    2681. 

  2681. <table class="docutils field-list" frame="void" rules="none">
    2682. 

  2682. <col class="field-name" />
    2683. 

  2683. <col class="field-body" />
    2684. 

  2684. <tbody valign="top">
    2685. 

  2685. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    2686. 

  2686. </tr>
    2687. 

  2687. </tbody>
    2688. 

  2688. </table>
    2689. 

  2689. <p><tt class="docutils literal"><span class="pre">function_output_iterator&amp;</span> <span class="pre">operator++(int);</span></tt></p>
    2690. 

  2690. <table class="docutils field-list" frame="void" rules="none">
    2691. 

  2691. <col class="field-name" />
    2692. 

  2692. <col class="field-body" />
    2693. 

  2693. <tbody valign="top">
    2694. 

  2694. <tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
    2695. 

  2695. </tr>
    2696. 

  2696. </tbody>
    2697. 

  2697. </table>
    2698. 

  2698. <!-- LocalWords:  Abrahams Siek Witt istream ostream iter MTL strided interoperate
    2699. 

  2699. LocalWords:  CRTP metafunctions inlining lvalue JGS incrementable BGL LEDA cv
    2700. 

  2700. LocalWords:  GraphBase struct ptrdiff UnaryFunction const int typename bool pp
    2701. 

  2701. LocalWords:  lhs rhs SFINAE markup iff tmp OtherDerived OtherIterator DWA foo
    2702. 

  2702. LocalWords:  dereferenceable subobject AdaptableUnaryFunction impl pre ifdef'd
    2703. 

  2703. LocalWords:  OtherIncrementable Coplien -->
    2704. 

  2704. </div>
    2705. 

  2705. </div>
    2706. 

  2706. </div>
    2707. 

  2707. </div>
    2708. 

  2708. </div>
    2709. 

  2709. <div class="footer">
    2710. 

  2710. <hr class="footer" />
    2711. 

  2711. <a class="reference external" href="facade-and-adaptor.rst">View document source</a>.
    2712. 

  2712. Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
    2713. 

  2713. 

  2714. </div>
    2715. 

  2715. </body>
    2716. 

  2716. </html>
    2717.