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  23. <div><h2 class="title">
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  24. <a name="boost_functional_overloadedfunction"></a>Chapter&#160;1.&#160;Boost.Functional/OverloadedFunction 1.0.0</h2></div>
    25. 

  25. <div><div class="author"><h3 class="author">
    26. 

  26. <span class="firstname">Lorenzo</span> <span class="surname">Caminiti <code class="email">&lt;<a class="email" href="mailto:lorcaminiti@gmail.com">lorcaminiti@gmail.com</a>&gt;</code></span>
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  27. </h3></div></div>
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  28. <div><p class="copyright">Copyright &#169; 2011, 2012 Lorenzo Caminiti</p></div>
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  30. <a name="boost_functional_overloadedfunction.legal"></a><p>
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  31.         Distributed under the Boost Software License, Version 1.0 (see accompanying
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  32.         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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  37. <p><b>Table of Contents</b></p>
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  38. <dl class="toc">
    39. 

  39. <dt><span class="section"><a href="index.html#boost_functional_overloadedfunction.introduction">Introduction</a></span></dt>
    40. 

  40. <dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html">Getting
    41. 

  41.     Started</a></span></dt>
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  42. <dd><dl>
    43. 

  43. <dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html#boost_functional_overloadedfunction.getting_started.compilers_and_platforms">Compilers
    44. 

  44.       and Platforms</a></span></dt>
    45. 

  45. <dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html#boost_functional_overloadedfunction.getting_started.installation">Installation</a></span></dt>
    46. 

  46. </dl></dd>
    47. 

  47. <dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html">Tutorial</a></span></dt>
    48. 

  48. <dd><dl>
    49. 

  49. <dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html#boost_functional_overloadedfunction.tutorial.overloading">Overloading</a></span></dt>
    50. 

  50. <dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html#boost_functional_overloadedfunction.tutorial.without_function_types">Without
    51. 

  51.       Function Types</a></span></dt>
    52. 

  52. </dl></dd>
    53. 

  53. <dt><span class="section"><a href="reference.html">Reference</a></span></dt>
    54. 

  54. <dt><span class="section"><a href="boost_functional_overloadedfunction/acknowledgments.html">Acknowledgments</a></span></dt>
    55. 

  55. </dl>
    56. 

  56. </div>
    57. 

  57. <p>
    58. 

  58.     This library allows to overload different functions into a single function object.
    59. 

  59.   </p>
    60. 

  60. <div class="section">
    61. 

  61. <div class="titlepage"><div><div><h2 class="title" style="clear: both">
    62. 

  62. <a name="boost_functional_overloadedfunction.introduction"></a><a class="link" href="index.html#boost_functional_overloadedfunction.introduction" title="Introduction">Introduction</a>
    63. 

  63. </h2></div></div></div>
    64. 

  64. <p>
    65. 

  65.       Consider the following functions which have distinct signatures:
    66. 

  66.     </p>
    67. 

  67. <p>
    68. 

  68. </p>
    69. 

  69. <pre class="programlisting"><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="identifier">identity_s</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="identifier">x</span><span class="special">)</span> <span class="comment">// Function (as pointer).</span>
    70. 

  70.     <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span>
    71. 

  71. 

  72. <span class="keyword">int</span> <span class="identifier">identity_i_impl</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span>
    73. 

  73. <span class="keyword">int</span> <span class="special">(&amp;</span><span class="identifier">identity_i</span><span class="special">)(</span><span class="keyword">int</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">identity_i_impl</span><span class="special">;</span> <span class="comment">// Function reference.</span>
    74. 

  74. 

  75. <span class="keyword">double</span> <span class="identifier">identity_d_impl</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span>
    76. 

  76. <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special">&lt;</span><span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">)&gt;</span> <span class="identifier">identity_d</span> <span class="special">=</span> <span class="identifier">identity_d_impl</span><span class="special">;</span> <span class="comment">// Functor.</span>
    77. 

  77. </pre>
    78. 

  78. <p>
    79. 

  79.     </p>
    80. 

  80. <p>
    81. 

  81.       Instead of calling them using their separate names (here <code class="computeroutput"><span class="identifier">BOOST_TEST</span></code>
    82. 

  82.       is equivalent to <code class="computeroutput"><span class="identifier">assert</span></code>):
    83. 

  83.       <a href="#ftn.boost_functional_overloadedfunction.introduction.f0" class="footnote" name="boost_functional_overloadedfunction.introduction.f0"><sup class="footnote">[1]</sup></a>
    84. 

  84.     </p>
    85. 

  85. <p>
    86. 

  86. </p>
    87. 

  87. <pre class="programlisting"><span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">identity_s</span><span class="special">(</span><span class="string">"abc"</span><span class="special">)</span> <span class="special">==</span> <span class="string">"abc"</span><span class="special">);</span>
    88. 

  88. <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">identity_i</span><span class="special">(</span><span class="number">123</span><span class="special">)</span> <span class="special">==</span> <span class="number">123</span><span class="special">);</span>
    89. 

  89. <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">identity_d</span><span class="special">(</span><span class="number">1.23</span><span class="special">)</span> <span class="special">==</span> <span class="number">1.23</span><span class="special">);</span>
    90. 

  90. </pre>
    91. 

  91. <p>
    92. 

  92.     </p>
    93. 

  93. <p>
    94. 

  94.       It is possible to use this library to create a single <a href="http://en.wikipedia.org/wiki/Function_overloading" target="_top">overloaded</a>
    95. 

  95.       function object (or <a href="http://en.wikipedia.org/wiki/Functor" target="_top">functor</a>)
    96. 

  96.       named <code class="computeroutput"><span class="identifier">identity</span></code> that aggregates
    97. 

  97.       together the calls to the specific functions (see also <a href="../../test/functor.cpp" target="_top"><code class="literal">functor.cpp</code></a>
    98. 

  98.       and <a href="../../test/identity.hpp" target="_top"><code class="literal">identity.hpp</code></a>):
    99. 

  99.     </p>
    100. 

  100. <p>
    101. 

  101. </p>
    102. 

  102. <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">overloaded_function</span><span class="special">&lt;</span>
    103. 

  103.       <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&amp;)</span>
    104. 

  104.     <span class="special">,</span> <span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)</span>
    105. 

  105.     <span class="special">,</span> <span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">)</span>
    106. 

  106. <span class="special">&gt;</span> <span class="identifier">identity</span><span class="special">(</span><span class="identifier">identity_s</span><span class="special">,</span> <span class="identifier">identity_i</span><span class="special">,</span> <span class="identifier">identity_d</span><span class="special">);</span>
    107. 

  107. 

  108. <span class="comment">// All calls via single `identity` function.</span>
    109. 

  109. <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">identity</span><span class="special">(</span><span class="string">"abc"</span><span class="special">)</span> <span class="special">==</span> <span class="string">"abc"</span><span class="special">);</span>
    110. 

  110. <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">identity</span><span class="special">(</span><span class="number">123</span><span class="special">)</span> <span class="special">==</span> <span class="number">123</span><span class="special">);</span>
    111. 

  111. <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">identity</span><span class="special">(</span><span class="number">1.23</span><span class="special">)</span> <span class="special">==</span> <span class="number">1.23</span><span class="special">);</span>
    112. 

  112. </pre>
    113. 

  113. <p>
    114. 

  114.     </p>
    115. 

  115. <p>
    116. 

  116.       Note how the functions are called via a single overloaded function object
    117. 

  117.       <code class="computeroutput"><span class="identifier">identity</span></code> instead of using their
    118. 

  118.       different names <code class="computeroutput"><span class="identifier">identity_s</span></code>,
    119. 

  119.       <code class="computeroutput"><span class="identifier">identity_i</span></code>, and <code class="computeroutput"><span class="identifier">identity_d</span></code>.
    120. 

  120.     </p>
    121. 

  121. </div>
    122. 

  122. <div class="footnotes">
    123. 

  123. <br><hr style="width:100; text-align:left;margin-left: 0">
    124. 

  124. <div id="ftn.boost_functional_overloadedfunction.introduction.f0" class="footnote"><p><a href="#boost_functional_overloadedfunction.introduction.f0" class="para"><sup class="para">[1] </sup></a>
    125. 

  125.         In most of the examples presented in this documentation, the Boost.Core/LightweightTest
    126. 

  126.         (<code class="literal">boost/core/lightweight_test.hpp</code>) macro <code class="computeroutput"><span class="identifier">BOOST_TEST</span></code> is used to check correctness
    127. 

  127.         conditions (conceptually similar to <code class="computeroutput"><span class="identifier">assert</span></code>).
    128. 

  128.         A failure of the checked condition does not abort the execution of the program,
    129. 

  129.         it will instead make <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span></code>
    130. 

  130.         return a non-zero program exit code. Using Boost.Core/LightweightTest allows
    131. 

  131.         to add the examples to the library regression tests so to make sure that
    132. 

  132.         they always compile and run correctly.
    133. 

  133.       </p></div>
    134. 

  134. </div>
    135. 

  135. </div>
    136. 

  136. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
    137. 

  137. <td align="left"><p><small>Last revised: December 05, 2018 at 20:06:59 GMT</small></p></td>
    138. 

  138. <td align="right"><div class="copyright-footer"></div></td>
    139. 

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    140. 

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