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| <div class="section"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <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 |
| static member function</a> |
| </h2></div></div></div> |
| <p> |
| The TTI macro <code class="computeroutput"><a class="link" href="../BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION.html" title="Macro BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</a></code> |
| introspects a static member function of a class. |
| </p> |
| <p> |
| BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION takes a single parameter which is the |
| name of an inner static member function whose existence the programmer wants |
| to check. The macro generates a metafunction called 'has_static_member_function_'name_of_inner_static_member_function'. |
| </p> |
| <p> |
| The metafunction can be invoked in two different ways. |
| </p> |
| <p> |
| The first way is by passing it the enclosing type to introspect and a signature |
| for the static member function as separate template arguments. The signature |
| for the static member 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 second way is by passing it the enclosing type to introspect and a signature |
| for the static member function as a function. The function has the form of: |
| </p> |
| <pre class="programlisting"><span class="identifier">Return_Type</span> <span class="special">(</span> <span class="identifier">Parameter_Types</span> <span class="special">)</span> |
| </pre> |
| <p> |
| where the Parameter_Types may be empty, or a comma-separated list of parameter |
| types if there are more than one parameter type. |
| </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 static member function, of the specified signature, exists |
| or not. |
| </p> |
| <h4> |
| <a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.h0"></a> |
| <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 |
| the metafunction</a> |
| </h4> |
| <p> |
| You generate the metafunction by invoking the macro with the name of an inner |
| static member function: |
| </p> |
| <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> |
| </pre> |
| <p> |
| generates a metafunction called 'has_static_member_function_AStaticMemberFunction' |
| in the current scope. |
| </p> |
| <h4> |
| <a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.h1"></a> |
| <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 |
| the metafunction</a> |
| </h4> |
| <p> |
| You invoke the metafunction by instantiating the template with an enclosing |
| type to introspect and the signature of the static member function as a series |
| of template parameters. Alternatively you can invoke the metafunction by passing |
| it an enclosing type and the signature of the static member function as a single |
| function type. |
| </p> |
| <p> |
| A return value called 'value' is a compile time bool constant. |
| </p> |
| <pre class="programlisting"><span class="identifier">has_static_member_function_AStaticMemberFunction</span> |
| <span class="special"><</span> |
| <span class="identifier">Enclosing_Type</span><span class="special">,</span> |
| <span class="identifier">StaticMemberFunction_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">StaticMemberFunction_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> |
| |
| <span class="identifier">OR</span> |
| |
| <span class="identifier">has_static_member_function_AStaticMemberFunction</span> |
| <span class="special"><</span> |
| <span class="identifier">Enclosing_Type</span><span class="special">,</span> |
| <span class="identifier">Return_Type</span> <span class="special">(</span> <span class="identifier">Parameter_Types</span> <span class="special">)</span> |
| <span class="special">>::</span><span class="identifier">value</span> |
| </pre> |
| <h4> |
| <a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.h2"></a> |
| <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> |
| </h4> |
| <p> |
| First we generate metafunctions for various inner static member 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_static_member_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">function1</span><span class="special">)</span> |
| <span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION</span><span class="special">(</span><span class="identifier">function2</span><span class="special">)</span> |
| <span class="identifier">BOOST_TTI_HAS_STATIC_MEMBER_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="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> |
| <span class="special">};</span> |
| <span class="keyword">struct</span> <span class="identifier">Top2</span> |
| <span class="special">{</span> |
| <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">&,</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> |
| <p> |
| We will show both forms in the following examples. Both forms are completely |
| interchangeable as to the result desired. |
| </p> |
| <pre class="programlisting"><span class="identifier">has_static_member_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_static_member_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_static_member_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_static_member_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_static_member_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_static_member_function_function2</span><span class="special"><</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">&,</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="identifier">value</span><span class="special">;</span> <span class="comment">// true</span> |
| |
| <span class="identifier">has_static_member_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_static_member_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="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="identifier">value</span><span class="special">;</span> <span class="comment">// true;</span> |
| </pre> |
| <h4> |
| <a name="the_type_traits_introspection_library.tti_detail_has_static_member_function.h3"></a> |
| <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 |
| re-use</a> |
| </h4> |
| <p> |
| The macro encodes only the name of the static member function for which we |
| are searching and the fact that we are introspecting for a static member function |
| within an enclosing type. |
| </p> |
| <p> |
| Because of this, once we create our metafunction for introspecting a static |
| member function by name, we can reuse the metafunction for introspecting any |
| enclosing type, having any static member function, for that name. |
| </p> |
| </div> |
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