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<h2><span class="refentrytitle">Struct template env_var</span></h2>
<p>boost::proto::functional::env_var —
A unary <a class="link" href="../../../PolymorphicFunctionObject.html" title="Concept PolymorphicFunctionObject">PolymorphicFunctionObject</a> used for fetching the value
associated with a particular key in a transform environment.
</p>
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<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.transform.env_hpp" title="Header <boost/proto/transform/env.hpp>">boost/proto/transform/env.hpp</a>>
</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Key<span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="env_var.html" title="Struct template env_var">env_var</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">// member classes/structs/unions</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Sig<span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="env_var/result.html" title="Struct template result">result</a> <span class="special">{</span>
<span class="comment">// <a class="link" href="env_var/result.html#boost.proto.functional.env_var.resulttypes">types</a></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 class="link" href="env_var/result.html#boost.proto.functional.env_var.result.type"><span class="identifier">type</span></a><span class="special">;</span>
<span class="special">}</span><span class="special">;</span>
<span class="comment">// <a class="link" href="env_var.html#idm45506990386624-bb">public member functions</a></span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Env<span class="special">></span> <em class="replaceable"><code><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></code></em> <a class="link" href="env_var.html#idm45506990386064-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">Env</span> <span class="keyword">const</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="idm45555173065184"></a><h2>Description</h2>
<div class="refsect2">
<a name="idm45555173064768"></a><h3>
<a name="idm45506990386624-bb"></a><code class="computeroutput">env_var</code> public member functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Env<span class="special">></span> <em class="replaceable"><code><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></code></em> <a name="idm45506990386064-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">Env</span> <span class="keyword">const</span> <span class="special">&</span> e<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<p>
This function behaves as follows:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
If <code class="computeroutput">Key</code> is <code class="computeroutput"><a class="link" href="../data_type.html" title="Struct data_type">proto::data_type</a></code>:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
If <code class="computeroutput"><a class="link" href="../is_env.html" title="Struct template is_env">proto::is_env</a><Env>::value</code> is <code class="computeroutput">true</code>,
return <code class="computeroutput">e[<a class="link" href="../data.html" title="Global data">proto::data</a>]</code>.
</li>
<li class="listitem">
Otherwise, return <code class="computeroutput">e</code>.
</li>
</ul></div>
</li>
<li class="listitem">
Otherwise, return <code class="computeroutput">e[Key()]</code>.
</li>
</ul></div>
<p>
</p>
<p>
See <code class="computeroutput"><a class="link" href="../env.html#idm45506990490160-bb">proto::env::operator[]</a></code> for additional information.
</p>
</li></ol></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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