<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Struct template is_callable</title> <link rel="stylesheet" href="../../boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> <link rel="up" href="../../proto/reference.html#header.boost.proto.traits_hpp" title="Header <boost/proto/traits.hpp>"> <link rel="prev" href="result_of/child_c.html" title="Struct template child_c"> <link rel="next" href="is_aggregate.html" title="Struct template is_aggregate"> </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="result_of/child_c.html"><img src="../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../proto/reference.html#header.boost.proto.traits_hpp"><img src="../../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="is_aggregate.html"><img src="../../../../doc/html/images/next.png" alt="Next"></a> </div> <div class="refentry" title="Struct template is_callable"> <a name="boost.proto.is_callable"></a><div class="titlepage"></div> <div class="refnamediv"> <h2><span class="refentrytitle">Struct template is_callable</span></h2> <p>boost::proto::is_callable — Boolean metafunction which tells whether a type is a callable <a class="link" href="../../PolymorphicFunctionObject.html" title="Concept PolymorphicFunctionObject">PolymorphicFunctionObject</a> or not.</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="emphasis"><em>// In header: <<a class="link" href="../../proto/reference.html#header.boost.proto.traits_hpp" title="Header <boost/proto/traits.hpp>">boost/proto/traits.hpp</a>> </em></span><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> T> <span class="bold"><strong>struct</strong></span> <a class="link" href="is_callable.html" title="Struct template is_callable">is_callable</a> : <span class="bold"><strong></strong></span> <span class="type">mpl::bool_<<em class="replaceable"><code><span class="bold"><strong>true</strong></span>-or-<span class="bold"><strong>false</strong></span></code></em>></span> { };</pre></div> <div class="refsect1" title="Description"> <a name="id1644002"></a><h2>Description</h2> <p> <code class="computeroutput">proto::is_callable<></code> is used by the <code class="computeroutput"><a class="link" href="when.html" title="Struct template when">proto::when<></a></code> transform to determine whether a function type <code class="computeroutput">R(A<sub>1</sub>,...A<sub>n</sub>)</code> is a <a class="link" href="../../CallableTransform.html" title="Concept CallableTransform">CallableTransform</a> or an <a class="link" href="../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a>. The former are evaluated using <code class="computeroutput"><a class="link" href="call.html" title="Struct template call">proto::call<></a></code> and the later with <code class="computeroutput"><a class="link" href="make.html" title="Struct template make">proto::make<></a></code>. If <code class="computeroutput">proto::is_callable<R>::value</code> is <code class="computeroutput">true</code>, the function type is a <a class="link" href="../../CallableTransform.html" title="Concept CallableTransform">CallableTransform</a>; otherwise, it is an <a class="link" href="../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a>. </p> <p> Unless specialized for a type <code class="computeroutput">T</code>, <code class="computeroutput">proto::is_callable<T>::value</code> is computed as follows: </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"><p> If <code class="computeroutput">T</code> is a template type <code class="computeroutput">X<Y<sub>0</sub>,...Y<sub>n</sub>></code>, where all <code class="computeroutput">Y<sub>x</sub></code> are types for <code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>, <code class="computeroutput">proto::is_callable<T>::value</code> is <code class="computeroutput">boost::is_same<Y<sub>n</sub>, <a class="link" href="callable.html" title="Struct callable">proto::callable</a>>::value</code>. </p></li> <li class="listitem"><p> If <code class="computeroutput">T</code> is derived from <code class="computeroutput"><a class="link" href="callable.html" title="Struct callable">proto::callable</a></code>, <code class="computeroutput">proto::is_callable<T>::value</code> is <code class="computeroutput">true</code>. </p></li> <li class="listitem"><p> Otherwise, <code class="computeroutput">proto::is_callable<T>::value</code> is <code class="computeroutput">false</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> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="result_of/child_c.html"><img src="../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../proto/reference.html#header.boost.proto.traits_hpp"><img src="../../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="is_aggregate.html"><img src="../../../../doc/html/images/next.png" alt="Next"></a> </div> </body> </html>