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boost_fusion/doc/html/fusion/support/is_view.html
Tobias Schwinger aaf89a67a6 updates functional module: only two unfused variants, now 
[SVN r51381]
2009-02-22 06:27:12 +00:00

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<title>is_view</title>
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<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="fusion.support.is_view"></a><a href="is_view.html" title="is_view">is_view</a></h3></div></div></div>
<a name="fusion.support.is_view.description"></a><h4>
<a name="id939445"></a>
<a href="is_view.html#fusion.support.is_view.description">Description</a>
</h4>
<p>
Metafunction that evaluates to <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>
if a certain type <code class="computeroutput"><span class="identifier">T</span></code> is a
conforming Fusion <a href="../view.html" title="View">View</a>, <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code>
otherwise. A view is a specialized sequence that does not actually contain
data. Views hold sequences which may be other views. In general, views are
held by other views by value, while non-views are held by other views by
reference. <code class="computeroutput"><span class="identifier">is_view</span></code> may be
specialized to accomodate clients providing Fusion conforming views.
</p>
<a name="fusion.support.is_view.synopsis"></a><h4>
<a name="id939542"></a>
<a href="is_view.html#fusion.support.is_view.synopsis">Synopsis</a>
</h4>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">traits</span>
<span class="special">{</span>
<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">is_view</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span> <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>
<span class="special">}</span>
</pre>
<a name="fusion.support.is_view.parameters"></a><h4>
<a name="id939658"></a>
<a href="is_view.html#fusion.support.is_view.parameters">Parameters</a>
</h4>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Requirement
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">T</span></code>
</p>
</td>
<td>
<p>
Any type
</p>
</td>
<td>
<p>
The type to query.
</p>
</td>
</tr></tbody>
</table></div>
<a name="fusion.support.is_view.expression_semantics"></a><h4>
<a name="id939751"></a>
<a href="is_view.html#fusion.support.is_view.expression_semantics">Expression Semantics</a>
</h4>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_view</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">c</span><span class="special">;</span>
</pre>
<p>
<span class="bold"><strong>Return type</strong></span>: An <a href="http://www.boost.org/libs/mpl/doc/refmanual/integral-constant.html" target="_top">MPL
Boolean Constant</a>.
</p>
<p>
<span class="bold"><strong>Semantics</strong></span>: Metafunction that evaluates to
<code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code> if a certain type <code class="computeroutput"><span class="identifier">T</span></code>
is a conforming Fusion view, <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span></code>
otherwise.
</p>
<a name="fusion.support.is_view.header"></a><h4>
<a name="id939900"></a>
<a href="is_view.html#fusion.support.is_view.header">Header</a>
</h4>
<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">fusion</span><span class="special">/</span><span class="identifier">support</span><span class="special">/</span><span class="identifier">is_view</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">is_view</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<a name="fusion.support.is_view.example"></a><h4>
<a name="id940036"></a>
<a href="is_view.html#fusion.support.is_view.example">Example</a>
</h4>
<pre class="programlisting"><span class="identifier">BOOST_MPL_ASSERT_NOT</span><span class="special">((</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_view</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="special">));</span>
<span class="identifier">BOOST_MPL_ASSERT_NOT</span><span class="special">((</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_view</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">));</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">_</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_pointer</span><span class="special">;</span>
<span class="keyword">typedef</span> <a href="../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special">&lt;</span><span class="keyword">int</span><span class="special">*,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">long</span><span class="special">*,</span> <span class="keyword">bool</span><span class="special">,</span> <span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">vector_type</span><span class="special">;</span>
<span class="keyword">typedef</span> <a href="../view/filter_view.html" title="filter_view"><code class="computeroutput"><span class="identifier">filter_view</span></code></a><span class="special">&lt;</span><span class="identifier">vector_type</span><span class="special">,</span> <span class="identifier">is_pointer</span><span class="special">&lt;</span><span class="identifier">_</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">filter_view_type</span><span class="special">;</span>
<span class="identifier">BOOST_MPL_ASSERT</span><span class="special">((</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_view</span><span class="special">&lt;</span><span class="identifier">filter_view_type</span><span class="special">&gt;</span> <span class="special">));</span>
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2007 Joel de Guzman, Dan Marsden, Tobias
Schwinger<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>)
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