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<div><h2 class="title">
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<a name="boost_functional_overloadedfunction"></a>Chapter 1. Boost.Functional/OverloadedFunction 1.0.0</h2></div>
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<div><div class="author"><h3 class="author">
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<span class="firstname">Lorenzo</span> <span class="surname">Caminiti <code class="email"><<a class="email" href="mailto:lorcaminiti@gmail.com">lorcaminiti@gmail.com</a>></code></span>
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<div><p class="copyright">Copyright © 2011, 2012 Lorenzo Caminiti</p></div>
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Distributed under the Boost Software License, Version 1.0 (see accompanying
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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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<p><b>Table of Contents</b></p>
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<dl class="toc">
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<dt><span class="section"><a href="index.html#boost_functional_overloadedfunction.introduction">Introduction</a></span></dt>
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<dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html">Getting
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Started</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html#boost_functional_overloadedfunction.getting_started.compilers_and_platforms">Compilers
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and Platforms</a></span></dt>
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<dt><span class="section"><a href="boost_functional_overloadedfunction/getting_started.html#boost_functional_overloadedfunction.getting_started.installation">Installation</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html">Tutorial</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html#boost_functional_overloadedfunction.tutorial.overloading">Overloading</a></span></dt>
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<dt><span class="section"><a href="boost_functional_overloadedfunction/tutorial.html#boost_functional_overloadedfunction.tutorial.without_function_types">Without
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Function Types</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="reference.html">Reference</a></span></dt>
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<dt><span class="section"><a href="boost_functional_overloadedfunction/acknowledgments.html">Acknowledgments</a></span></dt>
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</dl>
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</div>
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<p>
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This library allows to overload different functions into a single function object.
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</p>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="boost_functional_overloadedfunction.introduction"></a><a class="link" href="index.html#boost_functional_overloadedfunction.introduction" title="Introduction">Introduction</a>
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</h2></div></div></div>
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<p>
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Consider the following functions which have distinct signatures:
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</p>
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<p>
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</p>
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<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">&</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">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="comment">// Function (as pointer).</span>
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<span class="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span>
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<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>
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<span class="keyword">int</span> <span class="special">(&</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>
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<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>
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<span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">)></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>
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</pre>
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<p>
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</p>
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<p>
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Instead of calling them using their separate names (here <code class="computeroutput"><span class="identifier">BOOST_TEST</span></code>
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is equivalent to <code class="computeroutput"><span class="identifier">assert</span></code>):
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<a href="#ftn.boost_functional_overloadedfunction.introduction.f0" class="footnote" name="boost_functional_overloadedfunction.introduction.f0"><sup class="footnote">[1]</sup></a>
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</p>
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<p>
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</p>
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<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>
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<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>
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<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>
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</pre>
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<p>
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</p>
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<p>
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It is possible to use this library to create a single <a href="http://en.wikipedia.org/wiki/Function_overloading" target="_top">overloaded</a>
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function object (or <a href="http://en.wikipedia.org/wiki/Functor" target="_top">functor</a>)
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named <code class="computeroutput"><span class="identifier">identity</span></code> that aggregates
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together the calls to the specific functions (see also <a href="../../test/functor.cpp" target="_top"><code class="literal">functor.cpp</code></a>
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and <a href="../../test/identity.hpp" target="_top"><code class="literal">identity.hpp</code></a>):
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</p>
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<p>
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</p>
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<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">overloaded_function</span><span class="special"><</span>
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<span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</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">&)</span>
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<span class="special">,</span> <span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)</span>
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<span class="special">,</span> <span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">)</span>
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<span class="special">></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>
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<span class="comment">// All calls via single `identity` function.</span>
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<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>
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<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>
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<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>
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</pre>
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<p>
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</p>
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<p>
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Note how the functions are called via a single overloaded function object
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<code class="computeroutput"><span class="identifier">identity</span></code> instead of using their
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different names <code class="computeroutput"><span class="identifier">identity_s</span></code>,
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<code class="computeroutput"><span class="identifier">identity_i</span></code>, and <code class="computeroutput"><span class="identifier">identity_d</span></code>.
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</p>
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</div>
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<div class="footnotes">
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<br><hr style="width:100; text-align:left;margin-left: 0">
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<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>
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In most of the examples presented in this documentation, the Boost.Core/LightweightTest
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(<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
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conditions (conceptually similar to <code class="computeroutput"><span class="identifier">assert</span></code>).
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A failure of the checked condition does not abort the execution of the program,
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it will instead make <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span></code>
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return a non-zero program exit code. Using Boost.Core/LightweightTest allows
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to add the examples to the library regression tests so to make sure that
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they always compile and run correctly.
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</p></div>
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</div>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"><p><small>Last revised: April 13, 2021 at 16:29:22 GMT</small></p></td>
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