/Src/Dependencies/Boost/libs/mpl/doc/refmanual/if-c.html

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  7. <title>The MPL Reference Manual: if_c</title>
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  10. <body class="docframe refmanual">
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  11. <table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./if.html" class="navigation-link">Prev</a>&nbsp;<a href="./eval-if.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./if.html" class="navigation-link">Back</a>&nbsp;<a href="./eval-if.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./type-selection.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
    12. 

  12. <td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./metafunctions.html" class="navigation-link">Metafunctions</a> / <a href="./type-selection.html" class="navigation-link">Type Selection</a> / <a href="./if-c.html" class="navigation-link">if_c</a></td>
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  14. <div class="section" id="if-c">
    15. 

  15. <h1><a class="toc-backref" href="./type-selection.html#id1521">if_c</a></h1>
    16. 

  16. <div class="section" id="id866">
    17. 

  17. <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
    18. 

  18. <pre class="literal-block">
    19. 

  19. template&lt;
    20. 

  20.       bool c
    21. 

  21.     , typename T1
    22. 

  22.     , typename T2
    23. 

  23.     &gt;
    24. 

  24. struct <a href="./if-c.html" class="identifier">if_c</a>
    25. 

  25. {
    26. 

  26.     typedef <em>unspecified</em> type;
    27. 

  27. };
    28. 

  28. </pre>
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  29. </div>
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  30. <div class="section" id="id867">
    31. 

  31. <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
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  32. <p>Returns one of its two arguments, <tt class="literal"><span class="pre">T1</span></tt> or <tt class="literal"><span class="pre">T2</span></tt>, depending on the value of
    33. 

  33. integral constant <tt class="literal"><span class="pre">c</span></tt>. <tt class="literal"><span class="pre"><a href="./if-c.html" class="identifier">if_c</a>&lt;c,t1,t2&gt;::type</span></tt> is a shorcut notation for
    34. 

  34. <tt class="literal"><span class="pre"><a href="./if.html" class="identifier">if_</a>&lt;</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a>&lt;c&gt;,t1,t2</span> <span class="pre">&gt;::type</span></tt>.</p>
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  35. </div>
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  36. <div class="section" id="id868">
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  37. <h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
    38. 

  38. <pre class="literal-block">
    39. 

  39. #include &lt;<a href="../../../../boost/mpl/if.hpp" class="header">boost/mpl/if.hpp</a>&gt;
    40. 

  40. </pre>
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  41. </div>
    42. 

  42. <div class="section" id="id869">
    43. 

  43. <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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  44. <table border="1" class="docutils table">
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  45. <colgroup>
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  46. <col width="15%" />
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  47. <col width="36%" />
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  48. <col width="48%" />
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  49. </colgroup>
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  50. <thead valign="bottom">
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  51. <tr><th class="head">Parameter</th>
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  52. <th class="head">Requirement</th>
    53. 

  53. <th class="head">Description</th>
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  54. </tr>
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  55. </thead>
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  56. <tbody valign="top">
    57. 

  57. <tr><td><tt class="literal"><span class="pre">c</span></tt></td>
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  58. <td>An integral constant</td>
    59. 

  59. <td>A selection condition.</td>
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  60. </tr>
    61. 

  61. <tr><td><tt class="literal"><span class="pre">T1</span></tt>, <tt class="literal"><span class="pre">T2</span></tt></td>
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  62. <td>Any type</td>
    63. 

  63. <td>Types to select from.</td>
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  64. </tr>
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  65. </tbody>
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  66. </table>
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  67. </div>
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  68. <div class="section" id="id870">
    69. 

  69. <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
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  70. <p>For any integral constant <tt class="literal"><span class="pre">c</span></tt> and arbitrary types <tt class="literal"><span class="pre">t1</span></tt>, <tt class="literal"><span class="pre">t2</span></tt>:</p>
    71. 

  71. <pre class="literal-block">
    72. 

  72. typedef <a href="./if-c.html" class="identifier">if_c</a>&lt;c,t1,t2&gt;::type t;
    73. 

  73. </pre>
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  74. <table class="docutils field-list" frame="void" rules="none">
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  75. <col class="field-name" />
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  76. <col class="field-body" />
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  77. <tbody valign="top">
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  78. <tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td>
    79. 

  79. </tr>
    80. 

  80. <tr class="field"><th class="field-name">Semantics:</th><td class="field-body">Equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre"><a href="./if.html" class="identifier">if_</a>&lt;</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a>&lt;c&gt;,t1,t2</span> <span class="pre">&gt;::type</span> <span class="pre">t;</span></tt></td>
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  81. </tr>
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  82. </tbody>
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  83. </table>
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  84. </div>
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  85. <div class="section" id="id871">
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  86. <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
    87. 

  87. <pre class="literal-block">
    88. 

  88. typedef <a href="./if-c.html" class="identifier">if_c</a>&lt;true,char,long&gt;::type t1;
    89. 

  89. typedef <a href="./if-c.html" class="identifier">if_c</a>&lt;false,char,long&gt;::type t2;
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  90. 

  91. <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;t1, char&gt; ));
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  92. <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;t2, long&gt; ));
    93. 

  93. </pre>
    94. 

  94. <pre class="literal-block">
    95. 

  95. // allocates space for an object of class T on heap or &quot;inplace&quot;
    96. 

  96. // depending on its <a href="./size.html" class="identifier">size</a>
    97. 

  97. template&lt; typename T &gt; struct lightweight
    98. 

  98. {
    99. 

  99.     // ...
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  100.     typedef typename <a href="./if-c.html" class="identifier">if_c</a>&lt;
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  101.           sizeof(T) &lt;= sizeof(T*)
    102. 

  102.         , inplace_storage&lt;T&gt;
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  103.         , heap_storage&lt;T&gt;
    104. 

  104.         &gt;::type impl_t;
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  105. 

  106.     impl_t impl;
    107. 

  107. };
    108. 

  108. </pre>
    109. 

  109. </div>
    110. 

  110. <div class="section" id="id872">
    111. 

  111. <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
    112. 

  112. <p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./integral-constant.html">Integral Constant</a>, <a class="reference internal" href="./if.html">if_</a>, <a class="reference internal" href="./eval-if.html">eval_if</a>, <a class="reference internal" href="./bool.html">bool_</a></p>
    113. 

  113. <!-- Metafunctions/Type Selection//eval_if |30 -->
    114. 

  114. </div>
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  115. </div>
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  118. <table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./if.html" class="navigation-link">Prev</a>&nbsp;<a href="./eval-if.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./if.html" class="navigation-link">Back</a>&nbsp;<a href="./eval-if.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./type-selection.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
    119. 

  119. <td><div class="copyright-footer"><div class="copyright">Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams</div>
    120. 

  120. Distributed under the Boost Software License, Version 1.0. (See accompanying
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  121. file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body>
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