1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Chapter 1. Boost.Functional/OverloadedFunction 1.0.0</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="index.html" title="Chapter 1. Boost.Functional/OverloadedFunction 1.0.0"> 8<link rel="next" href="boost_functional_overloadedfunction/getting_started.html" title="Getting Started"> 9</head> 10<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 11<table cellpadding="2" width="100%"><tr> 12<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 13<td align="center"><a href="../../../../../index.html">Home</a></td> 14<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 15<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 16<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 17<td align="center"><a href="../../../../../more/index.htm">More</a></td> 18</tr></table> 19<hr> 20<div class="spirit-nav"><a accesskey="n" href="boost_functional_overloadedfunction/getting_started.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a></div> 21<div class="chapter"> 22<div class="titlepage"><div> 23<div><h2 class="title"> 24<a name="boost_functional_overloadedfunction"></a>Chapter 1. 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"><<a class="email" href="mailto:lorcaminiti@gmail.com">lorcaminiti@gmail.com</a>></code></span> 27</h3></div></div> 28<div><p class="copyright">Copyright © 2011, 2012 Lorenzo Caminiti</p></div> 29<div><div class="legalnotice"> 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> 34</div></div> 35</div></div> 36<div class="toc"> 37<p><b>Table of Contents</b></p> 38<dl class="toc"> 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<dt><span class="section"><a href="boost_functional_overloadedfunction/acknowledgments.html">Acknowledgments</a></span></dt> 55</dl> 56</div> 57<p> 58 This library allows to overload different functions into a single function object. 59 </p> 60<div class="section"> 61<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 62<a name="boost_functional_overloadedfunction.introduction"></a><a class="link" href="index.html#boost_functional_overloadedfunction.introduction" title="Introduction">Introduction</a> 63</h2></div></div></div> 64<p> 65 Consider the following functions which have distinct signatures: 66 </p> 67<p> 68</p> 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">&</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> 70 <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span> 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<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> 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<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> 77</pre> 78<p> 79 </p> 80<p> 81 Instead of calling them using their separate names (here <code class="computeroutput"><span class="identifier">BOOST_TEST</span></code> 82 is equivalent to <code class="computeroutput"><span class="identifier">assert</span></code>): 83 <a href="#ftn.boost_functional_overloadedfunction.introduction.f0" class="footnote" name="boost_functional_overloadedfunction.introduction.f0"><sup class="footnote">[1]</sup></a> 84 </p> 85<p> 86</p> 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<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<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</pre> 91<p> 92 </p> 93<p> 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 function object (or <a href="http://en.wikipedia.org/wiki/Functor" target="_top">functor</a>) 96 named <code class="computeroutput"><span class="identifier">identity</span></code> that aggregates 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 and <a href="../../test/identity.hpp" target="_top"><code class="literal">identity.hpp</code></a>): 99 </p> 100<p> 101</p> 102<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">overloaded_function</span><span class="special"><</span> 103 <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> 104 <span class="special">,</span> <span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)</span> 105 <span class="special">,</span> <span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">)</span> 106<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> 107 108<span class="comment">// All calls via single `identity` function.</span> 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<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<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</pre> 113<p> 114 </p> 115<p> 116 Note how the functions are called via a single overloaded function object 117 <code class="computeroutput"><span class="identifier">identity</span></code> instead of using their 118 different names <code class="computeroutput"><span class="identifier">identity_s</span></code>, 119 <code class="computeroutput"><span class="identifier">identity_i</span></code>, and <code class="computeroutput"><span class="identifier">identity_d</span></code>. 120 </p> 121</div> 122<div class="footnotes"> 123<br><hr style="width:100; text-align:left;margin-left: 0"> 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 In most of the examples presented in this documentation, the Boost.Core/LightweightTest 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 conditions (conceptually similar to <code class="computeroutput"><span class="identifier">assert</span></code>). 128 A failure of the checked condition does not abort the execution of the program, 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 return a non-zero program exit code. Using Boost.Core/LightweightTest allows 131 to add the examples to the library regression tests so to make sure that 132 they always compile and run correctly. 133 </p></div> 134</div> 135</div> 136<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 137<td align="left"><p><small>Last revised: August 11, 2020 at 15:01:10 GMT</small></p></td> 138<td align="right"><div class="copyright-footer"></div></td> 139</tr></table> 140<hr> 141<div class="spirit-nav"><a accesskey="n" href="boost_functional_overloadedfunction/getting_started.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a></div> 142</body> 143</html> 144
