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- <div class="titlepage"><div><div><h2 class="title" style="clear: both">
- <a name="the_type_traits_introspection_library.tti_detail_has_function"></a><a class="link" href="tti_detail_has_function.html" title="Introspecting an inner function">Introspecting
- an inner function</a>
- </h2></div></div></div>
- <p>
- The TTI macro <code class="computeroutput"><a class="link" href="../BOOST_TTI_HAS_FUNCTION.html" title="Macro BOOST_TTI_HAS_FUNCTION">BOOST_TTI_HAS_FUNCTION</a></code>
- introspects an inner function of a class. The function can be either a member
- function or a static member function.
- </p>
- <p>
- BOOST_TTI_HAS_FUNCTION takes a single parameter which is the name of an inner
- function whose existence the programmer wants to check. The macro generates
- a metafunction called "has_function_'name_of_inner_function'".
- </p>
- <p>
- The metafunction can be invoked by passing it the enclosing type to introspect
- and a signature for the function as separate template arguments. The signature
- for the function consists of a return type, optional parameter types in the
- form of a boost::mpl forward sequence of types, and an optional Boost FunctionTypes
- tag type. A typical boost::mpl forward sequence of types is a boost::mpl::vector<>.
- </p>
- <p>
- The metafunction returns a single type called 'type', which is a boost::mpl::bool_.
- As a convenience the metafunction returns the value of this type directly as
- a compile time bool constant called 'value'. This is true or false depending
- on whether the inner function, of the specified signature, exists or not.
- </p>
- <h4>
- <a name="the_type_traits_introspection_library.tti_detail_has_function.h0"></a>
- <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_function.generating_the_metafunction"></a></span><a class="link" href="tti_detail_has_function.html#the_type_traits_introspection_library.tti_detail_has_function.generating_the_metafunction">Generating
- the metafunction</a>
- </h4>
- <p>
- You generate the metafunction by invoking the macro with the name of an inner
- function:
- </p>
- <pre class="programlisting"><span class="identifier">BOOST_TTI_HAS_FUNCTION</span><span class="special">(</span><span class="identifier">AnInnerFunction</span><span class="special">)</span>
- </pre>
- <p>
- generates a metafunction called 'has_function_AnInnerFunction' in the current
- scope.
- </p>
- <h4>
- <a name="the_type_traits_introspection_library.tti_detail_has_function.h1"></a>
- <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_function.invoking_the_metafunction"></a></span><a class="link" href="tti_detail_has_function.html#the_type_traits_introspection_library.tti_detail_has_function.invoking_the_metafunction">Invoking
- the metafunction</a>
- </h4>
- <p>
- You invoke the metafunction by instantiating the template with an enclosing
- type to introspect and the signature of the function as a series of template
- parameters.
- </p>
- <p>
- A return value called 'value' is a compile time bool constant.
- </p>
- <pre class="programlisting"><span class="identifier">has_function_AnInnerFunction</span>
- <span class="special"><</span>
- <span class="identifier">Enclosing_Type</span><span class="special">,</span>
- <span class="identifier">Function_ReturnType</span><span class="special">,</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">Function_ParameterTypes</span><span class="special">>,</span> <span class="comment">// optional, can be any mpl forward sequence</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function_types</span><span class="special">::</span><span class="identifier">SomeTagType</span> <span class="comment">// optional, can be any FunctionTypes tag type</span>
- <span class="special">>::</span><span class="identifier">value</span>
- </pre>
- <h4>
- <a name="the_type_traits_introspection_library.tti_detail_has_function.h2"></a>
- <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_function.examples"></a></span><a class="link" href="tti_detail_has_function.html#the_type_traits_introspection_library.tti_detail_has_function.examples">Examples</a>
- </h4>
- <p>
- First we generate metafunctions for various inner function names:
- </p>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tti</span><span class="special">/</span><span class="identifier">has_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="identifier">BOOST_TTI_HAS_FUNCTION</span><span class="special">(</span><span class="identifier">function1</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_FUNCTION</span><span class="special">(</span><span class="identifier">function2</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_FUNCTION</span><span class="special">(</span><span class="identifier">function3</span><span class="special">)</span>
- </pre>
- <p>
- Next let us create some user-defined types we want to introspect.
- </p>
- <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">AClass</span> <span class="special">{</span> <span class="special">};</span>
- <span class="keyword">struct</span> <span class="identifier">Top</span>
- <span class="special">{</span>
- <span class="keyword">static</span> <span class="keyword">int</span> <span class="identifier">function1</span><span class="special">();</span>
- <span class="identifier">AClass</span> <span class="identifier">function2</span><span class="special">(</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">short</span> <span class="special">*);</span>
- <span class="special">};</span>
- <span class="keyword">struct</span> <span class="identifier">Top2</span>
- <span class="special">{</span>
- <span class="keyword">long</span> <span class="identifier">function2</span><span class="special">(</span><span class="identifier">Top</span> <span class="special">&,</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">bool</span><span class="special">,</span><span class="keyword">short</span><span class="special">,</span><span class="keyword">float</span><span class="special">);</span>
- <span class="keyword">static</span> <span class="identifier">Top</span> <span class="special">*</span> <span class="identifier">function3</span><span class="special">(</span><span class="keyword">long</span><span class="special">,</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">AClass</span> <span class="special">&);</span>
- <span class="special">};</span>
- </pre>
- <p>
- Finally we invoke our metafunction and return our value. This all happens at
- compile time, and can be used by programmers doing compile time template metaprogramming.
- </p>
- <pre class="programlisting"><span class="identifier">has_function_function1</span><span class="special"><</span><span class="identifier">Top</span><span class="special">,</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_function_function1</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">,</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_function_function2</span><span class="special"><</span><span class="identifier">Top</span><span class="special">,</span><span class="identifier">AClass</span><span class="special">,</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">short</span> <span class="special">*></span> <span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_function_function2</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">,</span><span class="identifier">AClass</span><span class="special">,</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">short</span> <span class="special">*></span> <span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_function_function3</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">,</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_function_function3</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">,</span><span class="identifier">Top</span> <span class="special">*,</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">long</span><span class="special">,</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">AClass</span> <span class="special">&></span> <span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true;</span>
- </pre>
- <h4>
- <a name="the_type_traits_introspection_library.tti_detail_has_function.h3"></a>
- <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_function.metafunction_re_use"></a></span><a class="link" href="tti_detail_has_function.html#the_type_traits_introspection_library.tti_detail_has_function.metafunction_re_use">Metafunction
- re-use</a>
- </h4>
- <p>
- The macro encodes only the name of the function for which we are searching
- and the fact that we are introspecting for a function within an enclosing type.
- </p>
- <p>
- Because of this, once we create our metafunction for introspecting a function
- by name, we can reuse the metafunction for introspecting any enclosing type,
- having any function, for that name.
- </p>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <td align="right"><div class="copyright-footer">Copyright © 2011-2013 Tropic Software
- East Inc<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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