123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211 |
- <html>
- <head>
- <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
- <title>Using the has_template_(xxx) metafunction</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 1. The Type Traits Introspection Library">
- <link rel="up" href="../tti_detail_has_template.html" title="Introspecting an inner class template">
- <link rel="prev" href="../tti_detail_has_template.html" title="Introspecting an inner class template">
- <link rel="next" href="../tti_detail_has_member_data.html" title="Introspecting member data">
- </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="../tti_detail_has_template.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tti_detail_has_template.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="../tti_detail_has_member_data.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
- </div>
- <div class="section">
- <div class="titlepage"><div><div><h3 class="title">
- <a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction"></a><a class="link" href="tti_detail_has_template_metafunction.html" title="Using the has_template_(xxx) metafunction">Using
- the has_template_(xxx) metafunction</a>
- </h3></div></div></div>
- <h5>
- <a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.h0"></a>
- <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.generating_the_metafunction"></a></span><a class="link" href="tti_detail_has_template_metafunction.html#the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.generating_the_metafunction">Generating
- the metafunction</a>
- </h5>
- <p>
- You generate the metafunction by invoking the macro with the name of an inner
- class template:
- </p>
- <pre class="programlisting"><span class="comment">// `template type parameters` form</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">AClassTemplate</span><span class="special">,</span><span class="identifier">BOOST_PP_NIL</span><span class="special">)</span> <span class="comment">// non-variadic macro</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">AClassTemplate</span><span class="special">)</span> <span class="comment">// variadic macro</span>
- <span class="comment">// `specific parameters` form</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">AClassTemplate</span><span class="special">,(</span><span class="number">2</span><span class="special">,(</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">int</span><span class="special">)))</span> <span class="comment">// non-variadic macro</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">AClassTemplate</span><span class="special">,</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">int</span><span class="special">)</span> <span class="comment">// variadic macro</span>
- </pre>
- <p>
- generates a metafunction called 'has_template_AClassTemplate' in the current
- scope.
- </p>
- <p>
- If you want to introspect the same class template name using both the <code class="computeroutput"><span class="keyword">template</span> <span class="identifier">type</span>
- <span class="identifier">parameters</span></code> form and the <code class="computeroutput"><span class="identifier">specific</span> <span class="identifier">parameters</span></code>
- form you will have the problem that you will be generating a metafunction
- of the same name and violating the C++ ODR rule. In this particular case
- you can use the alternate BOOST_TTI_TRAIT_HAS_TEMPLATE macro to name the
- particular metafunction which will be generated.
- </p>
- <h5>
- <a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.h1"></a>
- <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.invoking_the_metafunction"></a></span><a class="link" href="tti_detail_has_template_metafunction.html#the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.invoking_the_metafunction">Invoking
- the metafunction</a>
- </h5>
- <p>
- You invoke the metafunction by instantiating the template with an enclosing
- type to introspect. A return value called 'value' is a compile time bool
- constant.
- </p>
- <pre class="programlisting"><span class="identifier">has_template_AType</span><span class="special"><</span><span class="identifier">Enclosing_Type</span><span class="special">>::</span><span class="identifier">value</span>
- </pre>
- <h5>
- <a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.h2"></a>
- <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.examples"></a></span><a class="link" href="tti_detail_has_template_metafunction.html#the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.examples">Examples</a>
- </h5>
- <p>
- First we generate metafunctions for various inner class template 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_template</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="comment">// Using variadic macro, `template type parameters`</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template1</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template2</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template3</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template4</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template5</span><span class="special">)</span>
- <span class="comment">// or using non-variadic macro, `template type parameters`</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template1</span><span class="special">,</span><span class="identifier">BOOST_PP_NIL</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template2</span><span class="special">,</span><span class="identifier">BOOST_PP_NIL</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template3</span><span class="special">,</span><span class="identifier">BOOST_PP_NIL</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template4</span><span class="special">,</span><span class="identifier">BOOST_PP_NIL</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template5</span><span class="special">,</span><span class="identifier">BOOST_PP_NIL</span><span class="special">)</span>
- <span class="comment">// Using variadic macro, `specific parameters`</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template6</span><span class="special">,</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">int</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template7</span><span class="special">,</span><span class="keyword">typename</span><span class="special">,</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">class</span><span class="special">></span> <span class="keyword">struct</span><span class="special">,</span><span class="keyword">long</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template8</span><span class="special">,</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">typename</span><span class="special">)</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template9</span><span class="special">,</span><span class="keyword">typename</span><span class="special">,</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">typename</span><span class="special">,</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">typename</span><span class="special">,</span><span class="keyword">short</span><span class="special">)</span>
- <span class="comment">// or using non-variadic macro, `specific parameters`</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template6</span><span class="special">,(</span><span class="number">2</span><span class="special">,(</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">int</span><span class="special">)))</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template7</span><span class="special">,(</span><span class="number">4</span><span class="special">,(</span><span class="keyword">typename</span><span class="special">,</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">class</span><span class="special">></span> <span class="keyword">struct</span><span class="special">,</span><span class="keyword">long</span><span class="special">)))</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template8</span><span class="special">,(</span><span class="number">2</span><span class="special">,(</span><span class="keyword">double</span><span class="special">,</span><span class="keyword">typename</span><span class="special">)))</span>
- <span class="identifier">BOOST_TTI_HAS_TEMPLATE</span><span class="special">(</span><span class="identifier">Template9</span><span class="special">,(</span><span class="number">6</span><span class="special">,(</span><span class="keyword">typename</span><span class="special">,</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">typename</span><span class="special">,</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">typename</span><span class="special">,</span><span class="keyword">short</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">Top</span>
- <span class="special">{</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">X</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">Template1</span> <span class="special">{</span> <span class="special">};</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">B</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">C</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">Template2</span> <span class="special">{</span> <span class="special">};</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">B</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">C</span><span class="special">,</span><span class="keyword">int</span> <span class="identifier">D</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">Template3</span> <span class="special">{</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">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">B</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">C</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">D</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">Template3</span> <span class="special">{</span> <span class="special">};</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">X</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">Y</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">Template4</span> <span class="special">{</span> <span class="special">};</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">B</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">C</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">D</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">E</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">Template5</span> <span class="special">{</span> <span class="special">};</span>
- <span class="special">};</span>
- <span class="keyword">struct</span> <span class="identifier">Top3</span>
- <span class="special">{</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">X</span><span class="special">,</span><span class="keyword">int</span> <span class="identifier">Y</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">Template6</span> <span class="special">{</span> <span class="special">};</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">,</span><span class="keyword">class</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">B</span><span class="special">,</span><span class="keyword">long</span> <span class="identifier">C</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">Template7</span> <span class="special">{</span> <span class="special">};</span>
- <span class="special">};</span>
- <span class="keyword">struct</span> <span class="identifier">Top4</span>
- <span class="special">{</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">double</span> <span class="identifier">X</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">Y</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">Template8</span> <span class="special">{</span> <span class="special">};</span>
- <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">B</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">C</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">D</span><span class="special">,</span><span class="keyword">typename</span> <span class="identifier">E</span><span class="special">,</span><span class="keyword">short</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">Template9</span> <span class="special">{</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_template_Template1</span><span class="special"><</span><span class="identifier">Top</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_template_Template1</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_template_Template2</span><span class="special"><</span><span class="identifier">Top</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_template_Template2</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_template_Template3</span><span class="special"><</span><span class="identifier">Top</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false, not all typename/class template parameters</span>
- <span class="identifier">has_template_Template3</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_template_Template4</span><span class="special"><</span><span class="identifier">Top</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_template_Template4</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_template_Template5</span><span class="special"><</span><span class="identifier">Top</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_template_Template5</span><span class="special"><</span><span class="identifier">Top2</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_template_Template6</span><span class="special"><</span><span class="identifier">Top3</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_template_Template6</span><span class="special"><</span><span class="identifier">Top4</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_template_Template7</span><span class="special"><</span><span class="identifier">Top3</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_template_Template7</span><span class="special"><</span><span class="identifier">Top4</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_template_Template8</span><span class="special"><</span><span class="identifier">Top3</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_template_Template8</span><span class="special"><</span><span class="identifier">Top4</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- <span class="identifier">has_template_Template9</span><span class="special"><</span><span class="identifier">Top3</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// false</span>
- <span class="identifier">has_template_Template9</span><span class="special"><</span><span class="identifier">Top4</span><span class="special">>::</span><span class="identifier">value</span><span class="special">;</span> <span class="comment">// true</span>
- </pre>
- <h5>
- <a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.h3"></a>
- <span class="phrase"><a name="the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.metafunction_re_use"></a></span><a class="link" href="tti_detail_has_template_metafunction.html#the_type_traits_introspection_library.tti_detail_has_template.tti_detail_has_template_metafunction.metafunction_re_use">Metafunction
- re-use</a>
- </h5>
- <p>
- The macro encodes the name of the inner class template for which we are searching,
- the fact that we are introspecting for a class template within an enclosing
- type, and optionally the template parameters for that class template.
- </p>
- <p>
- Once we create our metafunction for introspecting an inner class template
- by name, we can reuse the metafunction for introspecting any enclosing type,
- having any inner class template, for that name.
- </p>
- <p>
- However we need to understand that we are restricted in our reuse of the
- metafunction by whether we originally use the template type parameters form
- or the specific form. In either case we are always introspecting an inner
- class template which matches that form. In the case of the template type
- parameters form, any inner class template for which we are introspecting
- must have all template type parameters, as well as the correct name. In the
- case of the specific parameters form, any inner class template for which
- we are introspecting must have template parameters which match the specific
- template parameters passed to the macro, as well as the correct 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>)
- </p>
- </div></td>
- </tr></table>
- <hr>
- <div class="spirit-nav">
- <a accesskey="p" href="../tti_detail_has_template.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tti_detail_has_template.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="../tti_detail_has_member_data.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
- </div>
- </body>
- </html>
|