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<div class="refentry">
<a name="boost.proto.matches"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Struct template matches</span></h2>
<p>boost::proto::matches — A Boolean metafunction that evaluates whether a given expression type matches a grammar.</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: <<a class="link" href="../../proto/reference.html#header.boost.proto.matches_hpp" title="Header <boost/proto/matches.hpp>">boost/proto/matches.hpp</a>>
</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <a class="link" href="../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> Grammar<span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="matches.html" title="Struct template matches">matches</a> <span class="special">:</span> <span class="keyword"></span> mpl::bool_<<em class="replaceable"><code>true-or-false</code></em>> <span class="special">{</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm45555184934272"></a><h2>Description</h2>
<p>
<code class="computeroutput">proto::matches<Expr, Grammar></code> inherits from
<code class="computeroutput">mpl::true_</code> if
<code class="computeroutput">Expr::proto_grammar</code> matches
<code class="computeroutput">Grammar::proto_grammar</code>, and from
<code class="computeroutput">mpl::false_</code> otherwise.
</p>
<p>
Non-terminal expressions are matched against a grammar according to the following rules:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
The wildcard pattern, <code class="computeroutput">
<a class="link" href="_.html" title="Struct _">proto::_</a>
</code>, matches any expression.
</p></li>
<li class="listitem"><p>
An expression
<code class="computeroutput">
<a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a><AT,
<a class="link" href="listN.html" title="Struct template listN">
proto::listN
</a><A<sub>0</sub>,...A<sub>n</sub>>
>
</code>
matches a grammar
<code class="computeroutput">
<a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a><BT,
<a class="link" href="listN.html" title="Struct template listN">
proto::listN
</a><B<sub>0</sub>,...B<sub>n</sub>>
>
</code> if
<code class="computeroutput">BT</code> is <code class="computeroutput">
<a class="link" href="_.html" title="Struct _">proto::_</a>
</code> or
<code class="computeroutput">AT</code>, and if <code class="computeroutput">
A<sub>x</sub>
</code> matches
<code class="computeroutput">
B<sub>x</sub>
</code> for each <code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>.
</p></li>
<li class="listitem"><p>
An expression
<code class="computeroutput">
<a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a><AT,
<a class="link" href="listN.html" title="Struct template listN">
proto::listN
</a><A<sub>0</sub>,...A<sub>n</sub>,U<sub>0</sub>,...U<sub>m</sub>>
>
</code> matches a grammar
<code class="computeroutput">
<a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a><BT,
<a class="link" href="listN.html" title="Struct template listN">
proto::listM
</a><B<sub>0</sub>,...B<sub>n</sub>,<a class="link" href="vararg.html" title="Struct template vararg">proto::vararg</a><V>
> >
</code> if
<code class="computeroutput">BT</code> is <code class="computeroutput">
<a class="link" href="_.html" title="Struct _">proto::_</a>
</code> or
<code class="computeroutput">AT</code>, and if
<code class="computeroutput">
A<sub>x</sub>
</code> matches
<code class="computeroutput">
B<sub>x</sub>
</code> for each
<code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code> and if
<code class="computeroutput">
U<sub>x</sub>
</code> matches
<code class="computeroutput">V</code> for each <code class="computeroutput">x</code> in
<code class="computeroutput">[0,m]</code>.
</p></li>
<li class="listitem"><p>
An expression <code class="computeroutput">E</code> matches
<code class="computeroutput">
<a class="link" href="or_.html" title="Struct template or_">proto::or_</a><B<sub>0</sub>,...B<sub>n</sub>>
</code> if
<code class="computeroutput">E</code> matches some
<code class="computeroutput">
B<sub>x</sub>
</code> for
<code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>.
</p></li>
<li class="listitem"><p>
An expression <code class="computeroutput">E</code> matches
<code class="computeroutput">
<a class="link" href="and_.html" title="Struct template and_">proto::and_</a><B<sub>0</sub>,...B<sub>n</sub>>
</code> if
<code class="computeroutput">E</code> matches all
<code class="computeroutput">
B<sub>x</sub>
</code> for
<code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>.
</p></li>
<li class="listitem">
<p>
An expression <code class="computeroutput">E</code> matches
<code class="computeroutput">
<a class="link" href="if_.html" title="Struct template if_">proto::if_</a><T,U,V>
</code> if:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<code class="computeroutput">
boost::result_of<<a class="link" href="when.html" title="Struct template when">proto::when</a><<a class="link" href="_.html" title="Struct _">proto::_</a>,T>(E)>::type::value
</code>
is <code class="computeroutput">true</code> and
<code class="computeroutput">E</code> matches
<code class="computeroutput">U</code>, <span class="emphasis"><em>or</em></span>
</li>
<li class="listitem">
<code class="computeroutput">
boost::result_of<<a class="link" href="when.html" title="Struct template when">proto::when</a><<a class="link" href="_.html" title="Struct _">proto::_</a>,T>(E)>::type::value
</code>
is <code class="computeroutput">false</code> and <code class="computeroutput">E</code> matches
<code class="computeroutput">V</code>.
</li>
</ul></div>
<p>
Note: <code class="computeroutput">U</code> defaults to <code class="computeroutput">
<a class="link" href="_.html" title="Struct _">proto::_</a>
</code>
and <code class="computeroutput">V</code> defaults to
<code class="computeroutput">
<a class="link" href="not_.html" title="Struct template not_">proto::not_</a><<a class="link" href="_.html" title="Struct _">proto::_</a>>
</code>.
</p>
</li>
<li class="listitem"><p>
An expression <code class="computeroutput">E</code> matches
<code class="computeroutput">
<a class="link" href="not_.html" title="Struct template not_">proto::not_</a><T>
</code> if
<code class="computeroutput">E</code> does <span class="emphasis"><em>not</em></span> match <code class="computeroutput">T</code>.
</p></li>
<li class="listitem"><p>
An expression <code class="computeroutput">E</code> matches
<code class="computeroutput">
<a class="link" href="switch_.html" title="Struct template switch_">proto::switch_</a><C, T>
</code> if
<code class="computeroutput">E</code> matches <code class="computeroutput">C::case_<boost::result_of<<a class="link" href="when.html" title="Struct template when">proto::when</a><<a class="link" href="_.html" title="Struct _">proto::_</a>,T>(E)>::type></code>.
Note: <code class="computeroutput">T</code> defaults to <code class="computeroutput"><a class="link" href="tag_of.html" title="Struct template tag_of">proto::tag_of</a><<a class="link" href="_.html" title="Struct _">proto::_</a>>()</code>
</p></li>
</ul></div>
<p>
</p>
<p>
A terminal expression can trivially match the grammar <a class="link" href="_.html" title="Struct _">proto::_</a>. In addition,
a terminal expression
<code class="computeroutput">
<a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a><AT,
<a class="link" href="term.html" title="Struct template term">proto::term</a><A> >
</code> matches a grammar
<code class="computeroutput">
<a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a><BT, <a class="link" href="term.html" title="Struct template term">proto::term</a><B> >
</code>
if <code class="computeroutput">BT</code> is <code class="computeroutput"><a class="link" href="_.html" title="Struct _">proto::_</a></code>
or <code class="computeroutput">AT</code> and one of the following is true:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
<code class="computeroutput">B</code> is the wildcard pattern,
<code class="computeroutput">
<a class="link" href="_.html" title="Struct _">proto::_</a>
</code>
</p></li>
<li class="listitem"><p>
<code class="computeroutput">A</code> is <code class="computeroutput">B</code>
</p></li>
<li class="listitem"><p>
<code class="computeroutput">A</code> is <code class="computeroutput">B &</code>
</p></li>
<li class="listitem"><p>
<code class="computeroutput">A</code> is <code class="computeroutput">B const &</code>
</p></li>
<li class="listitem"><p>
<code class="computeroutput">B</code> is <code class="computeroutput">
<a class="link" href="exact.html" title="Struct template exact">proto::exact</a><A>
</code>
</p></li>
<li class="listitem"><p>
<code class="computeroutput">B</code> is
<code class="computeroutput">
<a class="link" href="convertible_to.html" title="Struct template convertible_to">proto::convertible_to</a><X>
</code>
and <code class="computeroutput">boost::is_convertible<A,X>::value</code> is
<code class="computeroutput">true</code>.
</p></li>
<li class="listitem"><p>
<code class="computeroutput">A</code> is <code class="computeroutput">X[M]</code> or
<code class="computeroutput">X(&)[M]</code> and
<code class="computeroutput">B</code> is <code class="computeroutput">
X[<a class="link" href="N.html" title="Global N">proto::N</a>]
</code>.
</p></li>
<li class="listitem"><p>
<code class="computeroutput">A</code> is <code class="computeroutput">X(&)[M]</code>
and <code class="computeroutput">B</code> is <code class="computeroutput">
X(&)[<a class="link" href="N.html" title="Global N">proto::N</a>]
</code>.
</p></li>
<li class="listitem"><p>
<code class="computeroutput">A</code> is <code class="computeroutput">X[M]</code> or
<code class="computeroutput">X(&)[M]</code> and <code class="computeroutput">B</code> is
<code class="computeroutput">X*</code>.
</p></li>
<li class="listitem"><p>
<code class="computeroutput">B</code> <em class="replaceable"><code>lambda-matches</code></em>
<code class="computeroutput">A</code> (see below).
</p></li>
</ul></div>
<p>
</p>
<p>
A type <code class="computeroutput">B</code> <em class="replaceable"><code>lambda-matches</code></em>
<code class="computeroutput">A</code> if one of the following is true:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
<code class="computeroutput">B</code> is <code class="computeroutput">A</code>
</p></li>
<li class="listitem"><p>
<code class="computeroutput">B</code> is the wildcard pattern, <code class="computeroutput">
<a class="link" href="_.html" title="Struct _">proto::_</a>
</code>
</p></li>
<li class="listitem"><p>
<code class="computeroutput">B</code> is <code class="computeroutput">
T<B<sub>0</sub>,...B<sub>n</sub>>
</code> and <code class="computeroutput">A</code> is <code class="computeroutput">
T<A<sub>0</sub>,...A<sub>n</sub>>
</code> and for each <code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>,
<code class="computeroutput">A<sub>x</sub></code> and
<code class="computeroutput">B<sub>x</sub></code> are types such that
<code class="computeroutput">A<sub>x</sub></code> <em class="replaceable"><code>lambda-matches</code></em>
<code class="computeroutput">B<sub>x</sub></code>
</p></li>
</ul></div>
<p>
</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 © 2008 Eric Niebler<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>
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