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<a name="boost.proto.domain.as_child"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Struct template as_child</span></h2>
<p>boost::proto::domain::as_child —
A callable unary MonomorphicFunctionObject that specifies how objects are turned into
Proto expressions in this domain, for use in scenarios where the resulting expression is
intended to be made a child of another expression.
</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, for use in scenarios where
// the resulting expression is intended to be made a child of another
// expression.</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_child.html" title="Struct template as_child">as_child</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_child.result_type"></a><span class="identifier">result_type</span><span class="special">;</span>
<span class="comment">// <a class="link" href="as_child.html#idm45506996592432-bb">public member functions</a></span>
<span class="identifier">result_type</span> <a class="link" href="as_child.html#idm45506996591872-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="idm45555192214384"></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
as a child of another expression. In that scenario, it is usually
preferable to store child expressions by reference; or, in the case of objects that
are not yet Proto expressions, to wrap them by reference in a new Proto terminal
expression. (Contrast this description with the description for
<code class="computeroutput"><a class="link" href="as_expr.html" title="Struct template as_expr">proto::domain::as_expr</a></code>.)
</p>
<p>
The <code class="computeroutput">as_child</code> function object turns objects into
Proto expressions, if they are not already, by making them Proto terminals held by
reference. Objects that are already Proto expressions are simply returned by
reference. 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" style="list-style-type: disc; ">
<li class="listitem">
If <code class="computeroutput">T</code> is not a Proto expression type, the resulting
terminal is
<code class="computeroutput">Generator()(<em class="replaceable"><code>E</code></em><tag::terminal,
term< <code class="computeroutput">T &</code> > >::make(t))</code>.
</li>
<li class="listitem">
Otherwise, the result is the lvalue <code class="computeroutput">t</code>.
</li>
</ul></div>
<p>
</p>
<div class="refsect2">
<a name="idm45555192200128"></a><h3>
<a name="idm45506996592432-bb"></a><code class="computeroutput">as_child</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="idm45506996591872-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" class="variablelist compact">
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<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<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>
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