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  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="the_type_traits_introspection_library.tti_detail_has_member_function"></a><a class="link" href="tti_detail_has_member_function.html" title="Introspecting member function">Introspecting
  28     member function</a>
  29 </h2></div></div></div>
  30 <p>
  31       The TTI macro <code class="computeroutput"><a class="link" href="../BOOST_TT_idm46187185705488.html" title="Macro BOOST_TTI_HAS_MEMBER_FUNCTION">BOOST_TTI_HAS_MEMBER_FUNCTION</a></code>
  32       introspects a member function of a class.
  33     </p>
  34 <p>
  35       BOOST_TTI_HAS_MEMBER_FUNCTION takes a single parameter which is the name of
  36       an inner member function whose existence the programmer wants to check. The
  37       macro generates a metafunction called "has_member_function_'name_of_inner_member_function'".
  38     </p>
  39 <p>
  40       The metafunction can be invoked in two different ways.
  41     </p>
  42 <p>
  43       The first way of invoking the metafunction is by passing it the enclosing type
  44       to introspect and a signature for the member function as a series of separate
  45       template arguments. The signature for the member function consists of the template
  46       arguments of a return type, of optional parameter types in the form of a boost::mpl
  47       forward sequence of types, and of an optional Boost FunctionTypes tag type.
  48       A typical boost::mpl forward sequence of types is a boost::mpl::vector&lt;&gt;.
  49     </p>
  50 <p>
  51       The optional Boost FunctionTypes tag type may be used to specify cv-qualification.
  52       This means you can add 'const', 'volatile', or both by specifying an appropriate
  53       tag type. An alternate to using the tag type is to specify the enclosing type
  54       as 'const', 'volatile', or both. As an example if you specify the tag type
  55       as 'boost::function_types::const_qualified' or if you specify the enclosing
  56       type as 'const T', the member function which you are introspecting must be
  57       a const function.
  58     </p>
  59 <p>
  60       The second way of invoking the metafunction is by passing it a single parameter,
  61       which is a pointer to member function. This type has the form of:
  62     </p>
  63 <pre class="programlisting"><span class="identifier">Return_Type</span> <span class="special">(</span> <span class="identifier">Enclosing_Type</span><span class="special">::*</span> <span class="special">)</span> <span class="special">(</span> <span class="identifier">Parameter_Types</span> <span class="special">)</span> <span class="identifier">cv_qualifier</span><span class="special">(</span><span class="identifier">s</span><span class="special">)</span>
  64 </pre>
  65 <p>
  66       where the Parameter_Types may be empty, or a comma-separated list of parameter
  67       types if there are more than one parameter type. The cv-qualifier may be 'const',
  68       'volatile', or 'const volatile'.
  69     </p>
  70 <p>
  71       The metafunction returns a single type called 'type', which is a boost::mpl::bool_.
  72       As a convenience the metafunction returns the value of this type directly as
  73       a compile time bool constant called 'value'. This 'value' is true or false
  74       depending on whether the inner member function, of the specified signature,
  75       exists or not.
  76     </p>
  77 <h4>
  78 <a name="the_type_traits_introspection_library.tti_detail_has_member_function.h0"></a>
  79       <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_member_function.generating_the_metafunction"></a></span><a class="link" href="tti_detail_has_member_function.html#the_type_traits_introspection_library.tti_detail_has_member_function.generating_the_metafunction">Generating
  80       the metafunction</a>
  81     </h4>
  82 <p>
  83       You generate the metafunction by invoking the macro with the name of an inner
  84       member function:
  85     </p>
  86 <pre class="programlisting"><span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">AMemberFunction</span><span class="special">)</span>
  87 </pre>
  88 <p>
  89       generates a metafunction called 'has_member_function_AMemberFunction' in the
  90       current scope.
  91     </p>
  92 <h4>
  93 <a name="the_type_traits_introspection_library.tti_detail_has_member_function.h1"></a>
  94       <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_member_function.invoking_the_metafunction"></a></span><a class="link" href="tti_detail_has_member_function.html#the_type_traits_introspection_library.tti_detail_has_member_function.invoking_the_metafunction">Invoking
  95       the metafunction</a>
  96     </h4>
  97 <p>
  98       You invoke the metafunction by instantiating the template with an enclosing
  99       type to introspect and the signature of the member function as a series of
 100       template parameters. Alternatively you can invoke the metafunction by passing
 101       it a single type which is a pointer to member function.
 102     </p>
 103 <p>
 104       A return value called 'value' is a compile time bool constant.
 105     </p>
 106 <pre class="programlisting"><span class="identifier">has_member_function_AMemberFunction</span>
 107   <span class="special">&lt;</span>
 108   <span class="identifier">Enclosing_Type</span><span class="special">,</span>
 109   <span class="identifier">MemberFunction_ReturnType</span><span class="special">,</span>
 110   <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">&lt;</span><span class="identifier">MemberFunction_ParameterTypes</span><span class="special">&gt;,</span> <span class="comment">// optional, can be any mpl forward sequence</span>
 111   <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>
 112   <span class="special">&gt;::</span><span class="identifier">value</span>
 113
 114 <span class="identifier">OR</span>
 115
 116 <span class="identifier">has_member_function_AMemberFunction</span>
 117   <span class="special">&lt;</span>
 118   <span class="identifier">MemberFunction_ReturnType</span> <span class="special">(</span><span class="identifier">Enclosing_Type</span><span class="special">::*)</span> <span class="special">(</span><span class="identifier">MemberFunction_ParameterTypes</span><span class="special">)</span> <span class="identifier">optional_cv_qualification</span>
 119   <span class="special">&gt;::</span><span class="identifier">value</span>
 120 </pre>
 121 <h4>
 122 <a name="the_type_traits_introspection_library.tti_detail_has_member_function.h2"></a>
 123       <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_member_function.examples"></a></span><a class="link" href="tti_detail_has_member_function.html#the_type_traits_introspection_library.tti_detail_has_member_function.examples">Examples</a>
 124     </h4>
 125 <p>
 126       First we generate metafunctions for various inner member function names:
 127     </p>
 128 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tti</span><span class="special">/</span><span class="identifier">has_member_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 129
 130 <span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">function1</span><span class="special">)</span>
 131 <span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">function2</span><span class="special">)</span>
 132 <span class="identifier">BOOST_TTI_HAS_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">function3</span><span class="special">)</span>
 133 </pre>
 134 <p>
 135       Next let us create some user-defined types we want to introspect.
 136     </p>
 137 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">AClass</span>
 138   <span class="special">{</span>
 139   <span class="special">};</span>
 140 <span class="keyword">struct</span> <span class="identifier">Top</span>
 141   <span class="special">{</span>
 142   <span class="keyword">int</span> <span class="identifier">function1</span><span class="special">();</span>
 143   <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>
 144   <span class="special">};</span>
 145 <span class="keyword">struct</span> <span class="identifier">Top2</span>
 146   <span class="special">{</span>
 147   <span class="keyword">long</span> <span class="identifier">function2</span><span class="special">(</span><span class="identifier">Top</span> <span class="special">&amp;,</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>
 148   <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">&amp;);</span>
 149   <span class="special">};</span>
 150 </pre>
 151 <p>
 152       Finally we invoke our metafunction and return our value. This all happens at
 153       compile time, and can be used by programmers doing compile time template metaprogramming.
 154     </p>
 155 <p>
 156       We will show both forms in the following examples. Both forms are completely
 157       interchangeable as to the result desired.
 158     </p>
 159 <pre class="programlisting"><span class="identifier">has_member_function_function1</span><span class="special">&lt;</span><span class="identifier">Top</span><span class="special">,</span><span class="keyword">int</span><span class="special">&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
 160 <span class="identifier">has_member_function_function1</span><span class="special">&lt;</span><span class="identifier">Top</span><span class="special">,</span><span class="keyword">int</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">&lt;&gt;</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
 161 <span class="identifier">has_member_function_function1</span><span class="special">&lt;</span><span class="identifier">Top2</span><span class="special">,</span><span class="keyword">int</span><span class="special">&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
 162
 163 <span class="identifier">has_member_function_function2</span><span class="special">&lt;</span><span class="identifier">AClass</span> <span class="special">(</span><span class="identifier">Top</span><span class="special">::*)</span> <span class="special">(</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">short</span> <span class="special">*)&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
 164 <span class="identifier">has_member_function_function2</span><span class="special">&lt;</span><span class="identifier">AClass</span> <span class="special">(</span><span class="identifier">Top2</span><span class="special">::*)</span> <span class="special">(</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">short</span> <span class="special">*)&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
 165 <span class="identifier">has_member_function_function2</span><span class="special">&lt;</span><span class="keyword">long</span> <span class="special">(</span><span class="identifier">Top2</span><span class="special">::*)</span> <span class="special">(</span><span class="identifier">Top</span> <span class="special">&amp;,</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">)&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
 166
 167 <span class="identifier">has_member_function_function3</span><span class="special">&lt;</span><span class="keyword">int</span> <span class="special">(</span><span class="identifier">Top2</span><span class="special">::*)</span> <span class="special">()&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
 168 <span class="identifier">has_member_function_function3</span><span class="special">&lt;</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">&lt;</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">&amp;&gt;</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true;</span>
 169 </pre>
 170 <h4>
 171 <a name="the_type_traits_introspection_library.tti_detail_has_member_function.h3"></a>
 172       <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_member_function.metafunction_re_use"></a></span><a class="link" href="tti_detail_has_member_function.html#the_type_traits_introspection_library.tti_detail_has_member_function.metafunction_re_use">Metafunction
 173       re-use</a>
 174     </h4>
 175 <p>
 176       The macro encodes only the name of the member function for which we are searching
 177       and the fact that we are introspecting for a member function within an enclosing
 178       type.
 179     </p>
 180 <p>
 181       Because of this, once we create our metafunction for introspecting a member
 182       function by name, we can reuse the metafunction for introspecting any enclosing
 183       type, having any member function, for that name.
 184     </p>
 185 </div>
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