| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>Struct template as_expr</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="The Boost C++ Libraries BoostBook Documentation Subset"> |
| <link rel="up" href="../domain.html#id2274591" title="Description"> |
| <link rel="prev" href="../domain.html" title="Struct template domain"> |
| <link rel="next" href="as_child.html" title="Struct template as_child"> |
| </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="../domain.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../domain.html#id2274591"><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="as_child.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| <div class="refentry"> |
| <a name="boost.proto.domain.as_expr"></a><div class="titlepage"></div> |
| <div class="refnamediv"> |
| <h2><span class="refentrytitle">Struct template as_expr</span></h2> |
| <p>boost::proto::domain::as_expr — |
| A callable unary MonomorphicFunctionObject that specifies how objects are turned into |
| Proto expressions in this domain. The resulting expression object is suitable for storage |
| in a local variable. |
| </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.domain_hpp" title="Header <boost/proto/domain.hpp>">boost/proto/domain.hpp</a>> |
| |
| </span> |
| |
| <span class="comment">// A callable unary MonomorphicFunctionObject that specifies how objects are |
| // turned into Proto expressions in this domain. The resulting expression |
| // object is suitable for storage in a local variable.</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> |
| <span class="keyword">struct</span> <a class="link" href="as_expr.html" title="Struct template as_expr">as_expr</a> <span class="special">:</span> <span class="keyword"></span> <a class="link" href="../callable.html" title="Struct callable">proto::callable</a> <span class="special">{</span> |
| <span class="comment">// types</span> |
| <span class="keyword">typedef</span> <em class="replaceable"><code><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></code></em> <a name="boost.proto.domain.as_expr.result_type"></a><span class="identifier">result_type</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="as_expr.html#id1258448-bb">public member functions</a></span> |
| <span class="identifier">result_type</span> <a class="link" href="as_expr.html#id1258452-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">T</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="special">}</span><span class="special">;</span></pre></div> |
| <div class="refsect1"> |
| <a name="id2275268"></a><h2>Description</h2> |
| <p> |
| A unary MonomorphicFunctionObject that specifies how objects are turned into Proto |
| expressions in this domain. The resulting expression object is suitable for storage |
| in a local variable. In that scenario, it is usually preferable to return |
| expressions by value; and, in the case of objects that are not yet Proto expressions, |
| to wrap them by value (if possible) in a new Proto terminal expression. (Contrast |
| this description with the description for |
| <code class="computeroutput"><a class="link" href="as_child.html" title="Struct template as_child">proto::domain::as_child</a></code>.) |
| </p> |
| <p> |
| The <code class="computeroutput">as_expr</code> function object turns objects into |
| Proto expressions, if they are not already, by making them Proto terminals held by |
| value if possible. Objects that are already Proto expressions are simply returned |
| by value. If |
| <code class="computeroutput">wants_basic_expr<Generator>::value</code> is true, |
| then let <span class="emphasis"><em>E</em></span> be |
| <code class="computeroutput"><a class="link" href="../basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a></code>; |
| otherwise, let <span class="emphasis"><em>E</em></span> be |
| <code class="computeroutput"><a class="link" href="../expr.html" title="Struct template expr">proto::expr</a></code>. |
| Given an lvalue <code class="computeroutput">t</code> of type |
| <code class="computeroutput">T</code>: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| If <code class="computeroutput">T</code> is not a Proto expression type, the resulting |
| terminal is calculated as follows: |
| <div class="itemizedlist"><ul class="itemizedlist" type="circle"> |
| <li class="listitem"> |
| If <code class="computeroutput">T</code> is a function type, an abstract type, or |
| a type derived from <code class="computeroutput">std::ios_base</code>, let |
| <em class="replaceable"><code>A</code></em> be <code class="computeroutput">T &</code>. |
| </li> |
| <li class="listitem"> |
| Otherwise, let <em class="replaceable"><code>A</code></em> be the type |
| <code class="computeroutput">T</code> stripped of cv-qualifiers. |
| </li> |
| </ul></div> |
| Then, the result of <code class="computeroutput">as_expr<T>()(t)</code> is |
| <code class="computeroutput">Generator()(<em class="replaceable"><code>E</code></em><tag::terminal, |
| term< <em class="replaceable"><code>A</code></em> > >::make(t))</code>. |
| </li> |
| <li class="listitem"> |
| Otherwise, the result is <code class="computeroutput">t</code> converted to an |
| (un-const) rvalue. |
| </li> |
| </ul></div> |
| <p> |
| </p> |
| <div class="refsect2"> |
| <a name="id2275440"></a><h3> |
| <a name="id1258448-bb"></a><code class="computeroutput">as_expr</code> public member functions</h3> |
| <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> |
| <pre class="literallayout"><span class="identifier">result_type</span> <a name="id1258452-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&</span> t<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody><tr> |
| <td><p><span class="term">Parameters:</span></p></td> |
| <td><div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody><tr> |
| <td><p><span class="term"><code class="computeroutput">t</code></span></p></td> |
| <td><p>The object to wrap.</p></td> |
| </tr></tbody> |
| </table></div></td> |
| </tr></tbody> |
| </table></div> |
| </li></ol></div> |
| </div> |
| </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="../domain.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../domain.html#id2274591"><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="as_child.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |
