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  23 <div><h2 class="title">
  24 <a name="boost_functional_overloadedfunction"></a>Chapter&#160;1.&#160;Boost.Functional/OverloadedFunction 1.0.0</h2></div>
  25 <div><div class="author"><h3 class="author">
  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>
  27 </h3></div></div>
  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>
  31         Distributed under the Boost Software License, Version 1.0 (see accompanying
  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>)
  33       </p>
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  36 <div class="toc">
  37 <p><b>Table of Contents</b></p>
  38 <dl>
  39 <dt><span class="section"><a href="index.html#boost_functional_overloadedfunction.introduction">Introduction</a></span></dt>
  40 <dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html">Getting
  41     Started</a></span></dt>
  42 <dd><dl>
  43 <dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html#boost_functional_overloadedfunction.getting_started.compilers_and_platforms">Compilers
  44       and Platforms</a></span></dt>
  45 <dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html#boost_functional_overloadedfunction.getting_started.installation">Installation</a></span></dt>
  46 </dl></dd>
  47 <dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html">Tutorial</a></span></dt>
  48 <dd><dl>
  49 <dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html#boost_functional_overloadedfunction.tutorial.overloading">Overloading</a></span></dt>
  50 <dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html#boost_functional_overloadedfunction.tutorial.without_function_types">Without
  51       Function Types</a></span></dt>
  52 </dl></dd>
  53 <dt><span class="section"><a href="reference.html">Reference</a></span></dt>
  54 <dd><dl>
  55 <dt><span class="section"><a href="reference.html#header.boost.functional.overloaded_function_hpp">Header &lt;boost/functional/overloaded_function.hpp&gt;</a></span></dt>
  56 <dt><span class="section"><a href="reference.html#header.boost.functional.overloaded_function.config_hpp">Header &lt;boost/functional/overloaded_function/config.hpp&gt;</a></span></dt>
  57 </dl></dd>
  58 <dt><span class="section"><a href="boost_functional_overloadedfunction/acknowledgments.html">Acknowledgments</a></span></dt>
  59 </dl>
  60 </div>
  61 <p>
  62     This library allows to overload different functions into a single function object.
  63   </p>
  64 <div class="section boost_functional_overloadedfunction_introduction">
  65 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  66 <a name="boost_functional_overloadedfunction.introduction"></a><a class="link" href="index.html#boost_functional_overloadedfunction.introduction" title="Introduction">Introduction</a>
  67 </h2></div></div></div>
  68 <p>
  69       Consider the following functions which have distinct signatures:
  70     </p>
  71 <p>
  72 </p>
  73 <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>
  74     <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span>
  75
  76 <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>
  77 <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>
  78
  79 <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>
  80 <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>
  81 </pre>
  82 <p>
  83     </p>
  84 <p>
  85       Instead of calling them using their separate names (here <code class="computeroutput"><span class="identifier">BOOST_TEST</span></code>
  86       is equivalent to <code class="computeroutput"><span class="identifier">assert</span></code>):
  87       <sup>[<a name="boost_functional_overloadedfunction.introduction.f0" href="#ftn.boost_functional_overloadedfunction.introduction.f0" class="footnote">1</a>]</sup>
  88     </p>
  89 <p>
  90 </p>
  91 <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>
  92 <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>
  93 <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>
  94 </pre>
  95 <p>
  96     </p>
  97 <p>
  98       It is possible to use this library to create a single <a href="http://en.wikipedia.org/wiki/Function_overloading" target="_top">overloaded</a>
  99       function object (or <a href="http://en.wikipedia.org/wiki/Functor" target="_top">functor</a>)
 100       named <code class="computeroutput"><span class="identifier">identity</span></code> that aggregates
 101       together the calls to the specific functions (see also <a href="../../test/functor.cpp" target="_top"><code class="literal">functor.cpp</code></a>
 102       and <a href="../../test/identity.hpp" target="_top"><code class="literal">identity.hpp</code></a>):
 103     </p>
 104 <p>
 105 </p>
 106 <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">overloaded_function</span><span class="special">&lt;</span>
 107       <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>
 108     <span class="special">,</span> <span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)</span>
 109     <span class="special">,</span> <span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">)</span>
 110 <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>
 111
 112 <span class="comment">// All calls via single `identity` function.</span>
 113 <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>
 114 <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>
 115 <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>
 116 </pre>
 117 <p>
 118     </p>
 119 <p>
 120       Note how the functions are called via a single overloaded function object
 121       <code class="computeroutput"><span class="identifier">identity</span></code> instead of using their
 122       different names <code class="computeroutput"><span class="identifier">identity_s</span></code>,
 123       <code class="computeroutput"><span class="identifier">identity_i</span></code>, and <code class="computeroutput"><span class="identifier">identity_d</span></code>.
 124     </p>
 125 </div>
 126 <div class="footnotes">
 127 <br><hr width="100" align="left">
 128 <div class="footnote"><p><sup>[<a id="ftn.boost_functional_overloadedfunction.introduction.f0" href="#boost_functional_overloadedfunction.introduction.f0" class="para">1</a>] </sup>
 129         In most of the examples presented in this documentation, the Boost.Detail/LightweightTest
 130         (<code class="literal">boost/detail/lightweight_test.hpp</code>) macro <code class="computeroutput"><span class="identifier">BOOST_TEST</span></code> is used to check correctness
 131         conditions (conceptually similar to <code class="computeroutput"><span class="identifier">assert</span></code>).
 132         A failure of the checked condition does not abort the execution of the program,
 133         it will instead make <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span></code>
 134         return a non-zero program exit code. Using Boost.Detail/LightweightTest allows
 135         to add the examples to the library regression tests so to make sure that
 136         they always compile and run correctly.
 137       </p></div>
 138 </div>
 139 </div>
 140 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 141 <td align="left"><p><small>Last revised: April 28, 2012 at 02:19:13 GMT</small></p></td>
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