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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_static_member_function"></a><a class="link" href="tti_detail_has_static_member_function.html" title="Introspecting static member function">Introspecting
  28     static member function</a>
  29 </h2></div></div></div>
  30 <p>
  31       The TTI macro <code class="computeroutput"><a class="link" href="../BOOST_TT_idm46187185690608.html" title="Macro BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</a></code>
  32       introspects a static member function of a class.
  33     </p>
  34 <p>
  35       BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION takes a single parameter which is the
  36       name of an inner static member function whose existence the programmer wants
  37       to check. The macro generates a metafunction called "has_static_member_function_'name_of_inner_static_member_function'".
  38     </p>
  39 <p>
  40       The metafunction can be invoked in two different ways.
  41     </p>
  42 <p>
  43       The first way is by passing it the enclosing type to introspect and a signature
  44       for the static member function as separate template arguments. The signature
  45       for the static member function consists of a return type, optional parameter
  46       types in the form of a boost::mpl forward sequence of types, and an optional
  47       Boost FunctionTypes tag type. A typical boost::mpl forward sequence of types
  48       is a boost::mpl::vector&lt;&gt;.
  49     </p>
  50 <p>
  51       The second way is by passing it the enclosing type to introspect and a signature
  52       for the static member function as a function. The function has the form of:
  53     </p>
  54 <pre class="programlisting"><span class="identifier">Return_Type</span> <span class="special">(</span> <span class="identifier">Parameter_Types</span> <span class="special">)</span>
  55 </pre>
  56 <p>
  57       where the Parameter_Types may be empty, or a comma-separated list of parameter
  58       types if there are more than one parameter type.
  59     </p>
  60 <p>
  61       The metafunction returns a single type called 'type', which is a boost::mpl::bool_.
  62       As a convenience the metafunction returns the value of this type directly as
  63       a compile time bool constant called 'value'. This is true or false depending
  64       on whether the inner static member function, of the specified signature, exists
  65       or not.
  66     </p>
  67 <h4>
  68 <a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.h0"></a>
  69       <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.generating_the_metafunction"></a></span><a class="link" href="tti_detail_has_static_member_function.html#the_type_traits_introspection_library.tti_detail_has_static_member_function.generating_the_metafunction">Generating
  70       the metafunction</a>
  71     </h4>
  72 <p>
  73       You generate the metafunction by invoking the macro with the name of an inner
  74       static member function:
  75     </p>
  76 <pre class="programlisting"><span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">AStaticMemberFunction</span><span class="special">)</span>
  77 </pre>
  78 <p>
  79       generates a metafunction called 'has_static_member_function_AStaticMemberFunction'
  80       in the current scope.
  81     </p>
  82 <h4>
  83 <a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.h1"></a>
  84       <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.invoking_the_metafunction"></a></span><a class="link" href="tti_detail_has_static_member_function.html#the_type_traits_introspection_library.tti_detail_has_static_member_function.invoking_the_metafunction">Invoking
  85       the metafunction</a>
  86     </h4>
  87 <p>
  88       You invoke the metafunction by instantiating the template with an enclosing
  89       type to introspect and the signature of the static member function as a series
  90       of template parameters. Alternatively you can invoke the metafunction by passing
  91       it an enclosing type and the signature of the static member function as a single
  92       function type.
  93     </p>
  94 <p>
  95       A return value called 'value' is a compile time bool constant.
  96     </p>
  97 <pre class="programlisting"><span class="identifier">has_static_member_function_AStaticMemberFunction</span>
  98   <span class="special">&lt;</span>
  99   <span class="identifier">Enclosing_Type</span><span class="special">,</span>
 100   <span class="identifier">StaticMemberFunction_ReturnType</span><span class="special">,</span>
 101   <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">StaticMemberFunction_ParameterTypes</span><span class="special">&gt;,</span> <span class="comment">// optional, can be any mpl forward sequence</span>
 102   <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>
 103   <span class="special">&gt;::</span><span class="identifier">value</span>
 104
 105 <span class="identifier">OR</span>
 106
 107 <span class="identifier">has_static_member_function_AStaticMemberFunction</span>
 108   <span class="special">&lt;</span>
 109   <span class="identifier">Enclosing_Type</span><span class="special">,</span>
 110   <span class="identifier">Return_Type</span> <span class="special">(</span> <span class="identifier">Parameter_Types</span> <span class="special">)</span>
 111   <span class="special">&gt;::</span><span class="identifier">value</span>
 112 </pre>
 113 <h4>
 114 <a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.h2"></a>
 115       <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.examples"></a></span><a class="link" href="tti_detail_has_static_member_function.html#the_type_traits_introspection_library.tti_detail_has_static_member_function.examples">Examples</a>
 116     </h4>
 117 <p>
 118       First we generate metafunctions for various inner static member function names:
 119     </p>
 120 <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_static_member_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 121
 122 <span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">function1</span><span class="special">)</span>
 123 <span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">function2</span><span class="special">)</span>
 124 <span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">function3</span><span class="special">)</span>
 125 </pre>
 126 <p>
 127       Next let us create some user-defined types we want to introspect.
 128     </p>
 129 <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">AClass</span> <span class="special">{</span> <span class="special">};</span>
 130 <span class="keyword">struct</span> <span class="identifier">Top</span>
 131   <span class="special">{</span>
 132   <span class="keyword">static</span> <span class="keyword">int</span> <span class="identifier">function1</span><span class="special">();</span>
 133   <span class="keyword">static</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>
 134   <span class="special">};</span>
 135 <span class="keyword">struct</span> <span class="identifier">Top2</span>
 136   <span class="special">{</span>
 137   <span class="keyword">static</span> <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>
 138   <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">&amp;);</span>
 139   <span class="special">};</span>
 140 </pre>
 141 <p>
 142       Finally we invoke our metafunction and return our value. This all happens at
 143       compile time, and can be used by programmers doing compile time template metaprogramming.
 144     </p>
 145 <p>
 146       We will show both forms in the following examples. Both forms are completely
 147       interchangeable as to the result desired.
 148     </p>
 149 <pre class="programlisting"><span class="identifier">has_static_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>
 150 <span class="identifier">has_static_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>
 151 <span class="identifier">has_static_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>
 152
 153 <span class="identifier">has_static_member_function_function2</span><span class="special">&lt;</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">&lt;</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">short</span> <span class="special">*&gt;</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
 154 <span class="identifier">has_static_member_function_function2</span><span class="special">&lt;</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">&lt;</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">short</span> <span class="special">*&gt;</span> <span class="special">&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
 155 <span class="identifier">has_static_member_function_function2</span><span class="special">&lt;</span><span class="identifier">Top2</span><span class="special">,</span><span class="keyword">long</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>
 156
 157 <span class="identifier">has_static_member_function_function3</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>
 158 <span class="identifier">has_static_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="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;)&gt;::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true;</span>
 159 </pre>
 160 <h4>
 161 <a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.h3"></a>
 162       <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.metafunction_re_use"></a></span><a class="link" href="tti_detail_has_static_member_function.html#the_type_traits_introspection_library.tti_detail_has_static_member_function.metafunction_re_use">Metafunction
 163       re-use</a>
 164     </h4>
 165 <p>
 166       The macro encodes only the name of the static member function for which we
 167       are searching and the fact that we are introspecting for a static member function
 168       within an enclosing type.
 169     </p>
 170 <p>
 171       Because of this, once we create our metafunction for introspecting a static
 172       member function by name, we can reuse the metafunction for introspecting any
 173       enclosing type, having any static member function, for that name.
 174     </p>
 175 </div>
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