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<a name="boost.proto.unpack_e_idm45506975022288"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Function unpack_expr</span></h2>
<p>boost::proto::unpack_expr — Construct an expression of the requested tag type with a domain and with children
from the specified Fusion Forward Sequence.</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.make_expr_hpp" title="Header <boost/proto/make_expr.hpp>">boost/proto/make_expr.hpp</a>>
</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Tag<span class="special">,</span> <span class="keyword">typename</span> Sequence<span class="special">></span>
<span class="keyword">typename</span> <a class="link" href="result_of/unpack_expr.html" title="Struct template unpack_expr">proto::result_of::unpack_expr</a><span class="special"><</span><span class="identifier">Tag</span><span class="special">,</span> <span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span> <span class="keyword">const</span>
<span class="identifier">unpack_expr</span><span class="special">(</span><span class="identifier">Sequence</span> <span class="keyword">const</span> <span class="special">&</span> sequence<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Tag<span class="special">,</span> <span class="keyword">typename</span> <a class="link" href="../../Domain.html" title="Concept Domain">Domain</a><span class="special">,</span> <span class="keyword">typename</span> Sequence<span class="special">></span>
<span class="keyword">typename</span> <a class="link" href="result_of/unpack_expr.html" title="Struct template unpack_expr">proto::result_of::unpack_expr</a><span class="special"><</span><span class="identifier">Tag</span><span class="special">,</span> <span class="identifier">Domain</span><span class="special">,</span> <span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span> <span class="keyword">const</span>
<span class="identifier">unpack_expr</span><span class="special">(</span><span class="identifier">Sequence</span> <span class="keyword">const</span> <span class="special">&</span> sequence<span class="special">)</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm45555186059392"></a><h2>Description</h2>
<p>
This function template may be invoked either with or without specifying a
<code class="computeroutput">Domain</code> argument. If no domain is specified, the domain
is deduced by examining domains of each element of the sequence. See
<code class="computeroutput"><code class="computeroutput"><a class="link" href="deduce_domain.html" title="Struct deduce_domain">proto::deduce_domain</a></code></code> for a full
description of the procedure used.
</p>
<p>
Let <code class="computeroutput">s</code> be a Fusion RandomAccessSequence equivalent to
<code class="computeroutput">sequence</code>.
Let <code class="computeroutput"><em class="replaceable"><code>WRAP</code></em>(N, s)</code> be defined such that:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
If <code class="computeroutput">fusion::result_of::value_at_c<decltype(s),N>::type</code> is a reference type
or an instantiation of <code class="computeroutput">boost::reference_wrapper<></code>,
<code class="computeroutput"><em class="replaceable"><code>WRAP</code></em>(N, s)</code> is equivalent to
<code class="computeroutput"><code class="computeroutput"><a class="link" href="as_child_idm45506990983408.html" title="Function as_child">proto::as_child</a></code><Domain>(fusion::at_c<N>(s))</code>.
</p></li>
<li class="listitem"><p>
Otherwise, <code class="computeroutput"><em class="replaceable"><code>WRAP</code></em>(N, s)</code> is equivalent to
<code class="computeroutput"><code class="computeroutput"><a class="link" href="as_expr_idm45506991005376.html" title="Function as_expr">proto::as_expr</a></code><Domain>(fusion::at_c<N>(s))</code>.
</p></li>
</ul></div>
<p>
</p>
<p>
If <code class="computeroutput"><code class="computeroutput"><a class="link" href="wants_basic_expr.html" title="Struct template wants_basic_expr">proto::wants_basic_expr</a></code><typename Domain::proto_generator>::value</code>
is true, then let <code class="computeroutput"><em class="replaceable"><code>E</code></em></code> be
<code class="computeroutput"><code class="computeroutput"><a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a></code></code>; otherwise,
let <code class="computeroutput"><em class="replaceable"><code>E</code></em></code> be
<code class="computeroutput"><code class="computeroutput"><a class="link" href="expr.html" title="Struct template expr">proto::expr</a></code></code>.
</p>
<p>
Let <code class="computeroutput"><em class="replaceable"><code>MAKE</code></em>(Tag, b...)</code> be defined as
<code class="computeroutput"><em class="replaceable"><code>E</code></em><Tag,
<code class="computeroutput"><a class="link" href="listN.html" title="Struct template listN">proto::listN</a></code><decltype(b)...> >::make(b...)</code>.
</p>
<p>
If <code class="computeroutput">Tag</code> is
<code class="computeroutput"><code class="computeroutput"><a class="link" href="tag/terminal.html" title="Struct terminal">proto::tag::terminal</a></code></code>, then return
<code class="computeroutput"><em class="replaceable"><code>WRAP</code></em>(0, s)</code>.
</p>
<p>
Otherwise, return
<code class="computeroutput">Domain()(<em class="replaceable"><code>MAKE</code></em>(Tag, <em class="replaceable"><code>WRAP</code></em>(0, s),...
<em class="replaceable"><code>WRAP</code></em>(<em class="replaceable"><code>N</code></em>-1, s)))</code>, where
<em class="replaceable"><code>N</code></em> is the size of <code class="computeroutput">Sequence</code>.
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<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">sequence</code></span></p></td>
<td><p>A Fusion Forward Sequence.</p></td>
</tr></tbody>
</table></div></td>
</tr></tbody>
</table></div>
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<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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