devn00b
/
EQ2EMu


			
				
					
						
						
							1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192
							<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Macro BOOST_TTI_TRAIT_HAS_TYPE</title>
<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
<link rel="home" href="index.html" title="Chapter&#160;1.&#160;The Type Traits Introspection Library">
<link rel="up" href="header/boost/tti/has_type_hpp.html" title="Header &lt;boost/tti/has_type.hpp&gt;">
<link rel="prev" href="header/boost/tti/has_type_hpp.html" title="Header &lt;boost/tti/has_type.hpp&gt;">
<link rel="next" href="BOOST_TTI_HAS_TYPE.html" title="Macro BOOST_TTI_HAS_TYPE">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td>
<td align="center"><a href="../../../../index.html">Home</a></td>
<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="header/boost/tti/has_type_hpp.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="header/boost/tti/has_type_hpp.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="BOOST_TTI_HAS_TYPE.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="refentry">
<a name="BOOST_TTI_TRAIT_HAS_TYPE"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Macro BOOST_TTI_TRAIT_HAS_TYPE</span></h2>
<p>BOOST_TTI_TRAIT_HAS_TYPE</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="header/boost/tti/has_type_hpp.html" title="Header &lt;boost/tti/has_type.hpp&gt;">boost/tti/has_type.hpp</a>&gt;

</span>BOOST_TTI_TRAIT_HAS_TYPE(trait, name)</pre></div>
<div class="refsect1">
<a name="idm45456560396352"></a><h2>Description</h2>
<p>BOOST_TTI_TRAIT_HAS_TYPE is a macro which expands to a metafunction. The metafunction tests whether an inner type with a particular name exists and, optionally, whether a lambda expression invoked with the inner type is true or not.</p>
<p>trait = the name of the metafunction within the tti namespace.</p>
<p>name = the name of the inner type.</p>
<p>generates a metafunction called "trait" where 'trait' is the macro parameter.       template&lt;class BOOST_TTI_TP_T,class BOOST_TTI_TP_U&gt;
      struct trait
        {
        static const value = unspecified;
        typedef mpl::bool_&lt;true-or-false&gt; type;
        };

      The metafunction types and return:

        BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'.

        BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type.
                           If specified it is an MPL lambda expression which is invoked 
                           with the inner type found and must return a constant boolean 
                           value.

        returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified.

                  If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' type 
                  exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false.

                  If BOOST_TTI_TP_U is specified , then 'value' is true if the 'name' type exists 
                  within the enclosing type BOOST_TTI_TP_T and the lambda expression as specified 
                  by BOOST_TTI_TP_U, invoked by passing the actual inner type of 'name', returns 
                  a 'value' of true; otherwise 'value' is false.

                  The action taken with BOOST_TTI_TP_U occurs only when the 'name' type exists 
                  within the enclosing type BOOST_TTI_TP_T.
</p>
<p>Example usage:</p>
<p>BOOST_TTI_TRAIT_HAS_TYPE(LookFor,MyType) generates the metafunction LookFor in the current scope to look for an inner type called MyType.</p>
<p>LookFor&lt;EnclosingType&gt;::value is true if MyType is an inner type of EnclosingType, otherwise false.</p>
<p>LookFor&lt;EnclosingType,ALambdaExpression&gt;::value is true if MyType is an inner type of EnclosingType and invoking ALambdaExpression with the inner type returns a value of true, otherwise false.</p>
<p>A popular use of the optional MPL lambda expression is to check whether the type found is the same</p>
<p>as another type, when the type found is a typedef. In that case our example would be:</p>
<p>LookFor&lt;EnclosingType,boost::is_same&lt;_,SomeOtherType&gt; &gt;::value is true if MyType is an inner type of EnclosingType and is the same type as SomeOtherType. </p>
</div>
</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 &#169; 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>)
      </p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="header/boost/tti/has_type_hpp.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="header/boost/tti/has_type_hpp.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="BOOST_TTI_HAS_TYPE.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>