1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Struct template as_expr</title> 6<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../../../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../domain.html#id-1.3.33.5.9.4.4" title="Description"> 10<link rel="prev" href="../domain.html" title="Struct template domain"> 11<link rel="next" href="as_child.html" title="Struct template as_child"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 16<td align="center"><a href="../../../../../index.html">Home</a></td> 17<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="../domain.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../domain.html#id-1.3.33.5.9.4.4"><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> 25</div> 26<div class="refentry"> 27<a name="boost.proto.domain.as_expr"></a><div class="titlepage"></div> 28<div class="refnamediv"> 29<h2><span class="refentrytitle">Struct template as_expr</span></h2> 30<p>boost::proto::domain::as_expr — 31 A callable unary MonomorphicFunctionObject that specifies how objects are turned into 32 Proto expressions in this domain. The resulting expression object is suitable for storage 33 in a local variable. 34 </p> 35</div> 36<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> 37<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>> 38 39</span> 40 41<span class="comment">// A callable unary MonomorphicFunctionObject that specifies how objects are 42// turned into Proto expressions in this domain. The resulting expression 43// object is suitable for storage in a local variable.</span> 44<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> 45<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> 46 <span class="comment">// types</span> 47 <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> 48 49 <span class="comment">// <a class="link" href="as_expr.html#id-1_3_33_5_7_2_1_1_8_6-bb">public member functions</a></span> 50 <span class="identifier">result_type</span> <a class="link" href="as_expr.html#id-1_3_33_5_7_2_1_1_8_6_1-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> 51<span class="special">}</span><span class="special">;</span></pre></div> 52<div class="refsect1"> 53<a name="id-1.3.33.5.9.4.4.7.4"></a><h2>Description</h2> 54<p> 55 A unary MonomorphicFunctionObject that specifies how objects are turned into Proto 56 expressions in this domain. The resulting expression object is suitable for storage 57 in a local variable. In that scenario, it is usually preferable to return 58 expressions by value; and, in the case of objects that are not yet Proto expressions, 59 to wrap them by value (if possible) in a new Proto terminal expression. (Contrast 60 this description with the description for 61 <code class="computeroutput"><a class="link" href="as_child.html" title="Struct template as_child">proto::domain::as_child</a></code>.) 62 </p> 63<p> 64 The <code class="computeroutput">as_expr</code> function object turns objects into 65 Proto expressions, if they are not already, by making them Proto terminals held by 66 value if possible. Objects that are already Proto expressions are simply returned 67 by value. If 68 <code class="computeroutput">wants_basic_expr<Generator>::value</code> is true, 69 then let <span class="emphasis"><em>E</em></span> be 70 <code class="computeroutput"><a class="link" href="../basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a></code>; 71 otherwise, let <span class="emphasis"><em>E</em></span> be 72 <code class="computeroutput"><a class="link" href="../expr.html" title="Struct template expr">proto::expr</a></code>. 73 Given an lvalue <code class="computeroutput">t</code> of type 74 <code class="computeroutput">T</code>: 75 </p> 76<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 77<li class="listitem"> 78 If <code class="computeroutput">T</code> is not a Proto expression type, the resulting 79 terminal is calculated as follows: 80 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> 81<li class="listitem"> 82 If <code class="computeroutput">T</code> is a function type, an abstract type, or 83 a type derived from <code class="computeroutput">std::ios_base</code>, let 84 <em class="replaceable"><code>A</code></em> be <code class="computeroutput">T &</code>. 85 </li> 86<li class="listitem"> 87 Otherwise, let <em class="replaceable"><code>A</code></em> be the type 88 <code class="computeroutput">T</code> stripped of cv-qualifiers. 89 </li> 90</ul></div> 91 Then, the result of <code class="computeroutput">as_expr<T>()(t)</code> is 92 <code class="computeroutput">Generator()(<em class="replaceable"><code>E</code></em><tag::terminal, 93 term< <em class="replaceable"><code>A</code></em> > >::make(t))</code>. 94 </li> 95<li class="listitem"> 96 Otherwise, the result is <code class="computeroutput">t</code> converted to an 97 (un-const) rvalue. 98 </li> 99</ul></div> 100<p> 101 </p> 102<div class="refsect2"> 103<a name="id-1.3.33.5.9.4.4.7.4.4"></a><h3> 104<a name="id-1_3_33_5_7_2_1_1_8_6-bb"></a><code class="computeroutput">as_expr</code> public member functions</h3> 105<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"> 106<pre class="literallayout"><span class="identifier">result_type</span> <a name="id-1_3_33_5_7_2_1_1_8_6_1-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> 107<div class="variablelist"><table border="0" class="variablelist compact"> 108<colgroup> 109<col align="left" valign="top"> 110<col> 111</colgroup> 112<tbody><tr> 113<td><p><span class="term">Parameters:</span></p></td> 114<td><div class="variablelist"><table border="0" class="variablelist compact"> 115<colgroup> 116<col align="left" valign="top"> 117<col> 118</colgroup> 119<tbody><tr> 120<td><p><span class="term"><code class="computeroutput">t</code></span></p></td> 121<td><p>The object to wrap.</p></td> 122</tr></tbody> 123</table></div></td> 124</tr></tbody> 125</table></div> 126</li></ol></div> 127</div> 128</div> 129</div> 130<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 131<td align="left"></td> 132<td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<p> 133 Distributed under the Boost Software License, Version 1.0. (See accompanying 134 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>) 135 </p> 136</div></td> 137</tr></table> 138<hr> 139<div class="spirit-nav"> 140<a accesskey="p" href="../domain.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../domain.html#id-1.3.33.5.9.4.4"><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> 141</div> 142</body> 143</html> 144
