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<a name="boost.proto.operator_idm45506984344016"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Function operator,</span></h2>
<p>boost::proto::operator, —
For composing a larger transform environment from two smaller ones.
</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.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> Env<span class="special">,</span> <span class="keyword">typename</span> Key<span class="special">,</span> <span class="keyword">typename</span> Value<span class="special">></span>
<a class="link" href="env.html" title="Struct template env">proto::env</a><span class="special"><</span><span class="identifier">Key</span><span class="special">,</span> <span class="identifier">Value</span><span class="special">,</span> <em class="replaceable"><code><span class="identifier">UNCVREF</span></code></em><span class="special">(</span><span class="keyword">typename</span> <a class="link" href="result_of/as_env.html" title="Struct template as_env">proto::result_of::as_env</a><span class="special"><</span><span class="identifier">Env</span> <span class="special">&</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span><span class="special">)</span><span class="special">></span>
<span class="keyword">operator</span><span class="special">,</span><span class="special">(</span><span class="identifier">Env</span> <span class="special">&</span> other<span class="special">,</span> <a class="link" href="env.html" title="Struct template env">proto::env</a><span class="special"><</span><span class="identifier">Key</span><span class="special">,</span> <span class="identifier">Value</span><span class="special">></span> <span class="keyword">const</span> <span class="special">&</span> head<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Env<span class="special">,</span> <span class="keyword">typename</span> Key<span class="special">,</span> <span class="keyword">typename</span> Value<span class="special">></span>
<a class="link" href="env.html" title="Struct template env">proto::env</a><span class="special"><</span><span class="identifier">Key</span><span class="special">,</span> <span class="identifier">Value</span><span class="special">,</span> <em class="replaceable"><code><span class="identifier">UNCVREF</span></code></em><span class="special">(</span><span class="keyword">typename</span> <a class="link" href="result_of/as_env.html" title="Struct template as_env">proto::result_of::as_env</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="special">::</span><span class="identifier">type</span><span class="special">)</span><span class="special">></span>
<span class="keyword">operator</span><span class="special">,</span><span class="special">(</span><span class="identifier">Env</span> <span class="keyword">const</span> <span class="special">&</span> other<span class="special">,</span> <a class="link" href="env.html" title="Struct template env">proto::env</a><span class="special"><</span><span class="identifier">Key</span><span class="special">,</span> <span class="identifier">Value</span><span class="special">></span> <span class="keyword">const</span> <span class="special">&</span> head<span class="special">)</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm45555172588032"></a><h2>Description</h2>
<p>
The effect of this function is to take two transform environments and compose them into
a larger environment that contains the key/values pairs of the two. The first argument
is allowed to not be a transform environment, in which case it is turned into one with
the <code class="computeroutput"><a class="link" href="as_env_idm45506990359280.html" title="Function as_env">proto::as_env()</a></code> function before composition with the
second argument. The second argument is required to be a transform environment with exactly
one key/value pair.
</p>
<p>
<span class="bold"><strong>Example:</strong></span>
</p>
<p>
Given user-defined keys <code class="computeroutput">key0</code> and <code class="computeroutput">key1</code> of types <code class="computeroutput">key0_type</code>
and <code class="computeroutput">key1_type</code>, the following code demonstrates how the chained use of <code class="computeroutput">operator,</code>
can build a composite transform environment containing a number of key/value pairs:
</p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="env.html" title="Struct template env">proto::env</a></code><
key1_type
, int
, <code class="computeroutput"><a class="link" href="env.html" title="Struct template env">proto::env</a></code><
key0_type
, char const (&)[6]
, <code class="computeroutput"><a class="link" href="env.html" title="Struct template env">proto::env</a></code><<code class="computeroutput"><a class="link" href="data_type.html" title="Struct data_type">proto::data_type</a></code>, int>
>
> myenv = (<code class="computeroutput"><a class="link" href="data.html" title="Global data">proto::data</a></code> = 1, key0 = "hello", key1 = 42);
// NOTE: operator, here --^ and here --^
// Check the results:
assert(1 == myenv[proto::data]);
assert(0 == std::strcmp(myenv[key0], "hello"));
assert(42 == myenv[key1]);</pre>
<p>
</p>
<p>
<span class="bold"><strong>Note:</strong></span> In the return type and the "Returns" clause, <code class="computeroutput"><em class="replaceable"><code>UNCVREF</code></em>(X)</code> is
the type <code class="computeroutput">X</code> stripped of top-level reference and cv-qualifiers.
</p>
<p>
<span class="bold"><strong>Note:</strong></span> In the "Returns" clause, <code class="computeroutput"><em class="replaceable"><code>cv</code></em></code> is replaced with <code class="computeroutput">const</code>
for the second overload, and nothing for the first.
</p>
<p>
<span class="bold"><strong>See also:</strong></span>
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="computeroutput"><a class="link" href="env.html#idm45506990490160-bb">proto::env::operator[]</a></code></li></ul></div>
<p>
</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">Returns:</span></p></td>
<td><code class="computeroutput"><a class="link" href="env.html" title="Struct template env">proto::env</a><Key, Value, <em class="replaceable"><code>UNCVREF</code></em>(typename <a class="link" href="result_of/as_env.html" title="Struct template as_env">proto::result_of::as_env</a><Env <em class="replaceable"><code>cv</code></em> &>::type)>(head[Key()], <a class="link" href="as_env_idm45506990359280.html" title="Function as_env">proto::as_env</a>(other))</code></td>
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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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