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<div class="section boost_functional_overloadedfunction_Acknowledgments">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_functional_overloadedfunction.Acknowledgments"></a><a class="link" href="Acknowledgments.html" title="Acknowledgments">Acknowledgments</a>
</h2></div></div></div>
<p>
Many thanks to Mathias Gaunard for suggesting to implement <code class="computeroutput"><a class="link" href="../boost/overloaded_function.html" title="Class template overloaded_function">boost::overloaded_function</a></code>
and for some sample code.
</p>
<p>
Thanks to John Bytheway for suggesting to implement <code class="computeroutput"><a class="link" href="../boost/make_overloaded_function.html" title="Function template make_overloaded_function">boost::make_overloaded_function</a></code>.
</p>
<p>
Thanks to Nathan Ridge for suggestions on how to implement <code class="computeroutput"><a class="link" href="../boost/make_overloaded_function.html" title="Function template make_overloaded_function">boost::make_overloaded_function</a></code>.
</p>
<p>
Thanks to Robert Stewart for commenting on the library name.
</p>
<p>
Many thanks to the entire <a href="http://www.boost.org" target="_top">Boost</a> community
and mailing list for providing valuable comments about this library and great
insights on the C++ programming language.
</p>
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Distributed under the Boost Software License, Version 1.0 (see accompanying
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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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_functional_overloadedfunction.Getting_Started"></a><a class="link" href="Getting_Started.html" title="Getting Started">Getting
Started</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="Getting_Started.html#boost_functional_overloadedfunction.Getting_Started.compilers_and_platforms">Compilers
and Platforms</a></span></dt>
<dt><span class="section"><a href="Getting_Started.html#boost_functional_overloadedfunction.Getting_Started.installation">Installation</a></span></dt>
</dl></div>
<p>
This section explains how to setup a system to use this library.
</p>
<div class="section boost_functional_overloadedfunction_Getting_Started_compilers_and_platforms">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_functional_overloadedfunction.Getting_Started.compilers_and_platforms"></a><a class="link" href="Getting_Started.html#boost_functional_overloadedfunction.Getting_Started.compilers_and_platforms" title="Compilers and Platforms">Compilers
and Platforms</a>
</h3></div></div></div>
<p>
The library was tested by the authors on GCC 4.5.3 (with and without C++11
features <code class="literal">-std=c++0x</code>) and MSVC 8.0 under Linux, Cygwin,
and Windows 7.
</p>
</div>
<div class="section boost_functional_overloadedfunction_Getting_Started_installation">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_functional_overloadedfunction.Getting_Started.installation"></a><a class="link" href="Getting_Started.html#boost_functional_overloadedfunction.Getting_Started.installation" title="Installation">Installation</a>
</h3></div></div></div>
<p>
This library is composed of header files only. Therefore there is no pre-compiled
object file which needs to be installed. Programmers can simply instruct
the compiler where to find the library header files (<code class="computeroutput"><span class="special">-</span><span class="identifier">I</span></code> option on GCC, <code class="computeroutput"><span class="special">/</span><span class="identifier">I</span></code> option on MSVC, etc) and compile code
using the library.
</p>
<p>
The maximum number of functions to overload is given by the <code class="computeroutput"><a class="link" href="../BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX.html" title="Macro BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX">BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX</a></code>
configuration macro. The maximum number of function parameters for each of
the specified function types is given by the <code class="computeroutput"><a class="link" href="../BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_ARITY_MAX.html" title="Macro BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_ARITY_MAX">BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_ARITY_MAX</a></code>
configuration macro. All configuration macros have appropriate default values
when they are left undefined by the user.
</p>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2011, 2012 Lorenzo Caminiti<p>
Distributed under the Boost Software License, Version 1.0 (see accompanying
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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<div class="section boost_functional_overloadedfunction_Tutorial">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_functional_overloadedfunction.Tutorial"></a><a class="link" href="Tutorial.html" title="Tutorial">Tutorial</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="Tutorial.html#boost_functional_overloadedfunction.Tutorial.overloading">Overloading</a></span></dt>
<dt><span class="section"><a href="Tutorial.html#boost_functional_overloadedfunction.Tutorial.without_function_types">Without
Function Types</a></span></dt>
</dl></div>
<p>
This section explains how to use this library.
</p>
<div class="section boost_functional_overloadedfunction_Tutorial_overloading">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_functional_overloadedfunction.Tutorial.overloading"></a><a class="link" href="Tutorial.html#boost_functional_overloadedfunction.Tutorial.overloading" title="Overloading">Overloading</a>
</h3></div></div></div>
<p>
Consider the following functions with distinct signatures:
</p>
<p>
</p>
<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="special">{</span> <span class="keyword">return</span> <span class="identifier">x</span><span class="special">;</span> <span class="special">}</span> <span class="comment">// As pointer.</span>
<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>
<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>
<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>
<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>
</pre>
<p>
</p>
<p>
This library header <code class="computeroutput"><a class="link" href="../reference.html#header.boost.functional.overloaded_function_hpp" title="Header &lt;boost/functional/overloaded_function.hpp&gt;">boost/functional/overloaded_function.hpp</a></code>
provides a <code class="computeroutput"><a class="link" href="../boost/overloaded_function.html" title="Class template overloaded_function">boost::overloaded_function</a></code>
class template that creates a single overloaded function object that can
be used to call the specified functions instead of using the separate function
names (see also <a href="../../../test/identity.cpp" target="_top"><code class="literal">identity.cpp</code></a>):
</p>
<p>
</p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">overloaded_function</span><span class="special">&lt;</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="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="special">,</span> <span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)</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="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>
<span class="comment">// All calls via single `identity` function.</span>
<span class="identifier">BOOST_CHECK</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>
<span class="identifier">BOOST_CHECK</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>
<span class="identifier">BOOST_CHECK</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>
</pre>
<p>
</p>
<p>
Note how function types in the following format are passed as template parameters
to <code class="computeroutput"><a class="link" href="../boost/overloaded_function.html" title="Class template overloaded_function">boost::overloaded_function</a></code>
(this is the format of <a href="http://www.boost.org/libs/function" target="_top">Boost.Function</a>'s
preferred syntax):
</p>
<pre class="programlisting"><span class="emphasis"><em>result-type</em></span> <span class="special">(</span><span class="emphasis"><em>argument1-type</em></span><span class="special">,</span> <span class="emphasis"><em>argument2-type</em></span><span class="special">,</span> <span class="special">...)</span>
</pre>
<p>
Then the relative function pointers, function references, or <a href="http://en.wikipedia.org/wiki/Polymorphism_(computer_science)" target="_top">monomorphic
function</a> objects are passed to the <code class="computeroutput"><a class="link" href="../boost/overloaded_function.html" title="Class template overloaded_function">boost::overloaded_function</a></code>
constructor matching the order of the specified template parameters. <sup>[<a name="boost_functional_overloadedfunction.Tutorial.overloading.f0" href="#ftn.boost_functional_overloadedfunction.Tutorial.overloading.f0" class="footnote">2</a>]</sup> In the above example, <code class="computeroutput"><span class="identifier">identity_s</span></code>
is passed as function pointer (the function address is automatically taken
from the function name by compiler), <code class="computeroutput"><span class="identifier">identity_i</span></code>
as function reference, and <code class="computeroutput"><span class="identifier">identity_d</span></code>
as function object.
</p>
<p>
All specified function types must have distinct parameters from one another
(so the overloaded calls can be resolved by this library). <sup>[<a name="boost_functional_overloadedfunction.Tutorial.overloading.f1" href="#ftn.boost_functional_overloadedfunction.Tutorial.overloading.f1" class="footnote">3</a>]</sup> In order to create an overloaded function object, it is necessary
to specify at least two function types (because there is nothing to overload
between one or zero functions).
</p>
</div>
<div class="section boost_functional_overloadedfunction_Tutorial_without_function_types">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_functional_overloadedfunction.Tutorial.without_function_types"></a><a class="link" href="Tutorial.html#boost_functional_overloadedfunction.Tutorial.without_function_types" title="Without Function Types">Without
Function Types</a>
</h3></div></div></div>
<p>
For convenience, this library also provides the <code class="computeroutput"><a class="link" href="../boost/make_overloaded_function.html" title="Function template make_overloaded_function">boost::make_overloaded_function</a></code>
function template which allows to create the overloaded function object without
explicitly specifying the function types. The function types are automatically
deduced from the specified functions and the appropriate <code class="computeroutput"><a class="link" href="../boost/overloaded_function.html" title="Class template overloaded_function">boost::overloaded_function</a></code>
instantiation is returned by <code class="computeroutput"><a class="link" href="../boost/make_overloaded_function.html" title="Function template make_overloaded_function">boost::make_overloaded_function</a></code>.
</p>
<p>
The <code class="computeroutput"><a class="link" href="../boost/make_overloaded_function.html" title="Function template make_overloaded_function">boost::make_overloaded_function</a></code>
function template can be useful when used together with <a href="http://www.boost.org/doc/libs/typeof" target="_top">Boost.Typeof</a>'s
<code class="computeroutput"><span class="identifier">BOOST_AUTO</span></code> (or C++11 <code class="computeroutput"><span class="keyword">auto</span></code>). For example (see also <a href="../../../test/identity.cpp" target="_top"><code class="literal">identity.cpp</code></a>):
</p>
<p>
</p>
<pre class="programlisting"><span class="identifier">BOOST_AUTO</span><span class="special">(</span><span class="identifier">identity</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_overloaded_function</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>
<span class="identifier">BOOST_CHECK</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>
<span class="identifier">BOOST_CHECK</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>
<span class="identifier">BOOST_CHECK</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>
</pre>
<p>
</p>
<p>
Note how the overloaded function object <code class="computeroutput"><span class="identifier">identity</span></code>
has been created specifying only the functions <code class="computeroutput"><span class="identifier">identity_s</span></code>,
<code class="computeroutput"><span class="identifier">identity_i</span></code>, <code class="computeroutput"><span class="identifier">identity_d</span></code> and without specifying the function
types <code class="computeroutput"><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></code>,
<code class="computeroutput"><span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)</span></code>, and
<code class="computeroutput"><span class="keyword">double</span> <span class="special">(</span><span class="keyword">double</span><span class="special">)</span></code> as
required instead by <code class="computeroutput"><a class="link" href="../boost/overloaded_function.html" title="Class template overloaded_function">boost::overloaded_function</a></code>.
Therefore, <code class="computeroutput"><a class="link" href="../boost/make_overloaded_function.html" title="Function template make_overloaded_function">boost::make_overloaded_function</a></code>
provides a more concise syntax in this context when compared with <code class="computeroutput"><a class="link" href="../boost/overloaded_function.html" title="Class template overloaded_function">boost::overloaded_function</a></code>.
</p>
<p>
Another case where <code class="computeroutput"><a class="link" href="../boost/make_overloaded_function.html" title="Function template make_overloaded_function">boost::make_overloaded_function</a></code>
can be useful is when the overloaded function object is passed to a function
template which can hide the specific <code class="computeroutput"><a class="link" href="../boost/overloaded_function.html" title="Class template overloaded_function">boost::overloaded_function</a></code>
type using a template parameter. For example (see also <a href="../../../test/identity.cpp" target="_top"><code class="literal">identity.cpp</code></a>):
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">F</span><span class="special">&gt;</span>
<span class="keyword">void</span> <span class="identifier">check</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">identity</span><span class="special">)</span> <span class="special">{</span>
<span class="identifier">BOOST_CHECK</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>
<span class="identifier">BOOST_CHECK</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>
<span class="identifier">BOOST_CHECK</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>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
</p>
<pre class="programlisting"><span class="identifier">check</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_overloaded_function</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>
</pre>
<p>
</p>
</div>
<div class="footnotes">
<br><hr width="100" align="left">
<div class="footnote"><p><sup>[<a id="ftn.boost_functional_overloadedfunction.Tutorial.overloading.f0" href="#boost_functional_overloadedfunction.Tutorial.overloading.f0" class="para">2</a>] </sup>
Function pointers are of the form <code class="literal"><span class="emphasis"><em>result-type </em></span></code><code class="computeroutput"><span class="special">(*)(</span></code><code class="literal"><span class="emphasis"><em>argument1-type</em></span></code><code class="computeroutput"><span class="special">,</span> <span class="special">...)</span></code> (the
C++ compiler is usually able to automatically promote a function name to
a function pointer in a context where a function pointer is expected even
if the function name is not prefixed by <code class="computeroutput"><span class="special">&amp;</span></code>).
Function references are of the form <code class="literal"><span class="emphasis"><em>result-type </em></span></code><code class="computeroutput"><span class="special">(&amp;)(</span></code><code class="literal"><span class="emphasis"><em>argument1-type</em></span></code><code class="computeroutput"><span class="special">,</span> <span class="special">...)</span></code>.
Function types are of the form <code class="literal"><span class="emphasis"><em>result-type </em></span></code><code class="computeroutput"><span class="special">(</span></code><code class="literal"><span class="emphasis"><em>argument1-type</em></span></code><code class="computeroutput"><span class="special">,</span> <span class="special">...)</span></code> (note
how they lack of both <code class="computeroutput"><span class="special">*</span></code> and
<code class="computeroutput"><span class="special">&amp;</span></code> when compared to function
pointers and function references). Finally, monomorphic function objects
are instances of classes with a non-template call operator of the form
<code class="literal"><span class="emphasis"><em>result-type </em></span></code><code class="computeroutput"><span class="keyword">operator</span><span class="special">()(</span></code><code class="literal"><span class="emphasis"><em>argument1-type</em></span></code><code class="computeroutput"><span class="special">,</span> <span class="special">...)</span></code>.
</p></div>
<div class="footnote"><p><sup>[<a id="ftn.boost_functional_overloadedfunction.Tutorial.overloading.f1" href="#boost_functional_overloadedfunction.Tutorial.overloading.f1" class="para">3</a>] </sup>
Note that in C++ the function result type is not used for overload resolution
(to avoid making the overload resolution context dependent). Therefore,
at least one of the function parameters must be distinct for each specified
function type.
</p></div>
</div>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2011, 2012 Lorenzo Caminiti<p>
Distributed under the Boost Software License, Version 1.0 (see accompanying
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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