<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Struct template when<Grammar, R(A...)></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.transform.when_hpp" title="Header <boost/proto/transform/when.hpp>"> <link rel="prev" href="when_Grammar__Fun_id1272146.html" title="Struct template when<Grammar, Fun *>"> <link rel="next" href="when_Grammar__R_A___id1272228/impl.html" title="Struct template impl"> </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="when_Grammar__Fun_id1272146.html"><img src="../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../proto/reference.html#header.boost.proto.transform.when_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="when_Grammar__R_A___id1272228/impl.html"><img src="../../../../doc/html/images/next.png" alt="Next"></a> </div> <div class="refentry" title="Struct template when<Grammar, R(A...)>"> <a name="boost.proto.when_Grammar,_R(A_)_id1272228"></a><div class="titlepage"></div> <div class="refnamediv"> <h2><span class="refentrytitle">Struct template when<Grammar, R(A...)></span></h2> <p>boost::proto::when<Grammar, R(A...)> — A grammar element and a <a class="link" href="../../PrimitiveTransform.html" title="Concept PrimitiveTransform">PrimitiveTransform</a> that associates a transform with the 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="emphasis"><em>// In header: <<a class="link" href="../../proto/reference.html#header.boost.proto.transform.when_hpp" title="Header <boost/proto/transform/when.hpp>">boost/proto/transform/when.hpp</a>> </em></span><span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Grammar, <span class="bold"><strong>typename</strong></span> R, <span class="bold"><strong>typename</strong></span>... A> <span class="bold"><strong>struct</strong></span> <a class="link" href="when_Grammar__R_A___id1272228.html" title="Struct template when<Grammar, R(A...)>">when</a><Grammar, R(A...)> : <span class="bold"><strong></strong></span> <a class="link" href="transform.html" title="Struct template transform">proto::transform</a>< when<Grammar, R(A...)> > { <span class="emphasis"><em>// types</em></span> <span class="bold"><strong>typedef</strong></span> <span class="bold"><strong>typename</strong></span> Grammar::proto_base_expr <a name="boost.proto.when_Grammar,_R(A_)_id1272228.proto_base_expr"></a>proto_base_expr; <span class="emphasis"><em>// member classes/structs/unions</em></span> <span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> Expr, <span class="bold"><strong>typename</strong></span> State, <span class="bold"><strong>typename</strong></span> Data> <span class="bold"><strong>struct</strong></span> <a class="link" href="when_Grammar__R_A___id1272228/impl.html" title="Struct template impl">impl</a> : <span class="bold"><strong></strong></span> <a class="link" href="transform_impl.html" title="Struct template transform_impl">proto::transform_impl</a>< Expr, State, Data > { <span class="emphasis"><em>// types</em></span> <span class="bold"><strong>typedef</strong></span> <a class="link" href="call.html" title="Struct template call">proto::call</a><R(A...)> <a class="link" href="when_Grammar__R_A___id1272228/impl.html#boost.proto.when_Grammar,_R(A_)_id1272228.impl.call_">call_</a>; <span class="emphasis"><em>// For exposition only</em></span> <span class="bold"><strong>typedef</strong></span> <a class="link" href="make.html" title="Struct template make">proto::make</a><R(A...)> <a class="link" href="when_Grammar__R_A___id1272228/impl.html#boost.proto.when_Grammar,_R(A_)_id1272228.impl.make_">make_</a>; <span class="emphasis"><em>// For exposition only</em></span> <span class="bold"><strong>typedef</strong></span> <span class="bold"><strong>typename</strong></span> mpl::if_<<a class="link" href="is_callable.html" title="Struct template is_callable">proto::is_callable</a><R>,call_,make_>::type <a class="link" href="when_Grammar__R_A___id1272228/impl.html#boost.proto.when_Grammar,_R(A_)_id1272228.impl.which">which</a>; <span class="emphasis"><em>// For exposition only</em></span> <span class="bold"><strong>typedef</strong></span> <span class="bold"><strong>typename</strong></span> boost::result_of<which(Expr, State, Data)>::type <a class="link" href="when_Grammar__R_A___id1272228/impl.html#boost.proto.when_Grammar,_R(A_)_id1272228.impl.result_type">result_type</a>; <span class="emphasis"><em>// <a class="link" href="when_Grammar__R_A___id1272228/impl.html#id1272429-bb">public member functions</a></em></span> <span class="type">result_type</span> <a class="link" href="when_Grammar__R_A___id1272228/impl.html#id1272434-bb"><span class="bold"><strong>operator</strong></span>()</a>(<span class="bold"><strong>typename</strong></span> impl::expr_param, <span class="bold"><strong>typename</strong></span> impl::state_param, <span class="bold"><strong>typename</strong></span> impl::data_param) <span class="bold"><strong>const</strong></span>; }; };</pre></div> <div class="refsect1" title="Description"> <a name="id1678061"></a><h2>Description</h2> <p> Use <code class="computeroutput">proto::when<></code> to override a grammar's default transform with a custom transform. It is for use when composing larger transforms by associating smaller transforms with individual rules in your grammar. </p> <p> The <code class="computeroutput">when<G, R(A...)></code> form accepts either 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> as its second parameter. <code class="computeroutput">proto::when<></code> uses <code class="computeroutput"><a class="link" href="is_callable.html" title="Struct template is_callable">proto::is_callable</a><R>::value</code> to distinguish between the two, and uses <code class="computeroutput"><a class="link" href="call.html" title="Struct template call">proto::call<></a></code> to evaluate <a class="link" href="../../CallableTransform.html" title="Concept CallableTransform">CallableTransform</a>s and <code class="computeroutput"><a class="link" href="make.html" title="Struct template make">proto::make<></a></code> to evaluate <a class="link" href="../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a>s. </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="when_Grammar__Fun_id1272146.html"><img src="../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../proto/reference.html#header.boost.proto.transform.when_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="when_Grammar__R_A___id1272228/impl.html"><img src="../../../../doc/html/images/next.png" alt="Next"></a> </div> </body> </html>