<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>is_view</title> <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../../index.html" title="Chapter 1. Fusion 2.0"> <link rel="up" href="../support.html" title="Support"> <link rel="prev" href="is_sequence.html" title="is_sequence"> <link rel="next" href="tag_of.html" title="tag_of"> </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="is_sequence.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../support.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="tag_of.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="fusion.support.is_view"></a><a class="link" href="is_view.html" title="is_view">is_view</a> </h3></div></div></div> <a name="fusion.support.is_view.description"></a><h5> <a name="id877627"></a> <a class="link" href="is_view.html#fusion.support.is_view.description">Description</a> </h5> <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 class="link" 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><h5> <a name="id877692"></a> <a class="link" href="is_view.html#fusion.support.is_view.synopsis">Synopsis</a> </h5> <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"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></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><h5> <a name="id877786"></a> <a class="link" href="is_view.html#fusion.support.is_view.parameters">Parameters</a> </h5> <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><h5> <a name="id877873"></a> <a class="link" href="is_view.html#fusion.support.is_view.expression_semantics">Expression Semantics</a> </h5> <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"><</span><span class="identifier">T</span><span class="special">>::</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><h5> <a name="id877987"></a> <a class="link" href="is_view.html#fusion.support.is_view.header">Header</a> </h5> <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</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">></span> <span class="preprocessor">#include</span> <span class="special"><</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">></span> </pre> <a name="fusion.support.is_view.example"></a><h5> <a name="id878095"></a> <a class="link" href="is_view.html#fusion.support.is_view.example">Example</a> </h5> <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"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></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"><</span><span class="keyword">int</span><span class="special">></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 class="link" href="../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><</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">></span> <span class="identifier">vector_type</span><span class="special">;</span> <span class="keyword">typedef</span> <a class="link" href="../view/filter_view.html" title="filter_view"><code class="computeroutput"><span class="identifier">filter_view</span></code></a><span class="special"><</span><span class="identifier">vector_type</span><span class="special">,</span> <span class="identifier">is_pointer</span><span class="special"><</span><span class="identifier">_</span><span class="special">></span> <span class="special">></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"><</span><span class="identifier">filter_view_type</span><span class="special">></span> <span class="special">));</span> </pre> </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 © 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>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="is_sequence.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../support.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="tag_of.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>