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<title>Struct template impl</title>
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<div class="refentry">
<a name="boost.proto.make.impl"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Struct template impl</span></h2>
<p>boost::proto::make::impl</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.make_hpp" title="Header <boost/proto/transform/make.hpp>">boost/proto/transform/make.hpp</a>>
</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <a class="link" href="../../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> State<span class="special">,</span> <span class="keyword">typename</span> Data<span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="impl.html" title="Struct template impl">impl</a> <span class="special">:</span> <span class="keyword"></span> <a class="link" href="../transform_impl.html" title="Struct template transform_impl">proto::transform_impl</a><span class="special"><</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span> <span class="special">></span> <span class="special">{</span>
<span class="comment">// <a class="link" href="impl.html#boost.proto.make.impltypes">types</a></span>
<span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></em></span> <a class="link" href="impl.html#boost.proto.make.impl.result_type"><span class="identifier">result_type</span></a><span class="special">;</span>
<span class="comment">// <a class="link" href="impl.html#idp68860280-bb">public member functions</a></span>
<span class="identifier">result_type</span> <a class="link" href="impl.html#idp68860568-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">expr_param</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">state_param</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">data_param</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="idp187618312"></a><h2>Description</h2>
<div class="refsect2">
<a name="idp187618520"></a><h3>
<a name="boost.proto.make.impltypes"></a><code class="computeroutput">impl</code>
public
types</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<p>
<span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">see</span><span class="special">-</span><span class="identifier">below</span></em></span> <a name="boost.proto.make.impl.result_type"></a><span class="identifier">result_type</span><span class="special">;</span></p>
<p>
<code class="computeroutput"><a class="link" href="../make.html" title="Struct template make">proto::make</a><T>::impl<Expr, State, Data>::result_type</code> is
computed as follows:
</p>
<p>
If <code class="computeroutput">T</code> is an <a class="link" href="../../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a> of the form
<code class="computeroutput">Object(A<sub>0</sub>,…A<sub>n</sub>)</code> or
<code class="computeroutput">Object(A<sub>0</sub>,…A<sub>n</sub> ...)</code>,
then let <code class="computeroutput">O</code> be the return type
<code class="computeroutput">Object</code>. Otherwise, let <code class="computeroutput">O</code>
be <code class="computeroutput">T</code>. The <code class="computeroutput">result_type</code> typedef is
then computed as follows:
</p>
<p>
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
If <code class="computeroutput"><a class="link" href="../is_transform.html" title="Struct template is_transform">proto::is_transform</a><O>::value</code> is
<code class="computeroutput">true</code>, then let the result type be
<code class="computeroutput">
boost::result_of<<a class="link" href="../when.html" title="Struct template when">proto::when</a><<a class="link" href="../_.html" title="Struct _">_</a>, O>(Expr, State, Data)>::type
</code>.
Note that a substitution took place.
</p></li>
<li class="listitem">
If <code class="computeroutput">O</code> is a template like
<code class="computeroutput"><a class="link" href="../noinvoke.html" title="Struct template noinvoke">proto::noinvoke</a><S<X<sub>0</sub>,…X<sub>n</sub>> ></code>,
then the result type is calculated as follows:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem"><p>
For each <code class="computeroutput">i</code> in
<code class="computeroutput">[0,n]</code>, let <code class="computeroutput">
X<sub>i</sub>'
</code> be
<code class="computeroutput">
boost::result_of<<a class="link" href="../make.html" title="Struct template make">proto::make</a><X<sub>i</sub>>(Expr, State, Data)>::type
</code>
(which evaluates this procedure recursively). Note that a substitution took place. (In this case,
Proto merely assumes that a substitution took place for the sake of compile-time efficiency. There
would be no reason to use <code class="computeroutput"><a class="link" href="../noinvoke.html" title="Struct template noinvoke">proto::noinvoke<></a></code>
otherwise.)
</p></li>
<li class="listitem"><p>
The result type is
<code class="computeroutput">
S<X<sub>0</sub>',…X<sub>n</sub>'>
</code>.
</p></li>
</ul></div>
</li>
<li class="listitem">
If <code class="computeroutput">O</code> is a template like
<code class="computeroutput">S<X<sub>0</sub>,…X<sub>n</sub>></code>,
then the result type is calculated as follows:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem"><p>
For each <code class="computeroutput">i</code> in
<code class="computeroutput">[0,n]</code>, let <code class="computeroutput">
X<sub>i</sub>'
</code> be
<code class="computeroutput">
boost::result_of<<a class="link" href="../make.html" title="Struct template make">proto::make</a><X<sub>i</sub>>(Expr, State, Data)>::type
</code>
(which evaluates this procedure recursively). Note whether any substitutions took place during
this operation.
</p></li>
<li class="listitem"><p>
If any substitutions took place in the above step and
<code class="computeroutput">
S<X<sub>0</sub>',…X<sub>n</sub>'>
</code> has a nested
<code class="computeroutput">type</code> typedef, the result type is
<code class="computeroutput">
S<X<sub>0</sub>',…X<sub>n</sub>'>::type
</code>.
</p></li>
<li class="listitem"><p>
Otherwise, the result type is
<code class="computeroutput">
S<X<sub>0</sub>',…X<sub>n</sub>'>
</code>.
</p></li>
</ul></div>
</li>
<li class="listitem">
Otherwise, the result type is <code class="computeroutput">O</code>, and note that no
substitution took place.
</li>
</ul></div>
<p>
</p>
<p>
Note that <code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when<></a></code> is implemented
in terms of <code class="computeroutput"><a class="link" href="../call.html" title="Struct template call">proto::call<></a></code>
and <code class="computeroutput"><a class="link" href="../make.html" title="Struct template make">proto::make<></a></code>, so the
above procedure is evaluated recursively.
</p>
</li></ol></div>
</div>
<div class="refsect2">
<a name="idp187650024"></a><h3>
<a name="idp68860280-bb"></a><code class="computeroutput">impl</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="idp68860568-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">expr_param</span> expr<span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">state_param</span> state<span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">impl</span><span class="special">::</span><span class="identifier">data_param</span> data<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<p>
<code class="computeroutput">
<code class="computeroutput"><a class="link" href="../make.html" title="Struct template make">proto::make</a></code><T>::impl<Expr,State,Data>::operator()
</code>
behaves as follows:
</p>
<p>
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If <code class="computeroutput">T</code> is of the form
<code class="computeroutput">O(A<sub>0</sub>,…A<sub>n</sub>)</code>, then:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p>
If <code class="computeroutput">
<code class="computeroutput"><a class="link" href="../is_aggregate.html" title="Struct template is_aggregate">proto::is_aggregate</a></code><result_type>::value
</code> is <code class="computeroutput">true</code>, then construct
and return an object <code class="computeroutput">that</code> as follows:
</p>
<pre class="programlisting">result_type that = {
<code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when</a></code><<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, A<sub>0</sub>>()(expr, state, data),
…
<code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when</a></code><<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, A<sub>n</sub>>()(expr, state, data)
};</pre>
<p>
</p>
</li>
<li class="listitem">
<p>
Otherwise, construct
and return an object <code class="computeroutput">that</code> as follows:
</p>
<pre class="programlisting">result_type that(
<code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when</a></code><<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, A<sub>0</sub>>()(expr, state, data),
…
<code class="computeroutput"><a class="link" href="../when.html" title="Struct template when">proto::when</a></code><<code class="computeroutput"><a class="link" href="../_.html" title="Struct _">_</a></code>, A<sub>n</sub>>()(expr, state, data)
);</pre>
<p>
</p>
</li>
</ul></div>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">T</code> is of the form
<code class="computeroutput">O(A<sub>0</sub>,…A<sub>n</sub> ...)</code>,
then let <code class="computeroutput">T'</code> be <code class="computeroutput">O(A<sub>0</sub>,…A<sub>n-1</sub>, <em class="replaceable"><code>S</code></em>)</code>,
where <em class="replaceable"><code>S</code></em> is a type sequence computed from the unpacking expression <code class="computeroutput">A<sub>n</sub></code>
as described in the reference for <code class="computeroutput"><code class="computeroutput"><a class="link" href="../pack.html" title="Struct pack">proto::pack</a></code></code>. Then, return:
</p>
<pre class="programlisting">proto::make<T'>()(expr, state, data)</pre>
<p>
</p>
</li>
<li class="listitem">
<p>
Otherwise, construct and return an object <code class="computeroutput">that</code>
as follows: </p>
<pre class="programlisting">result_type that = result_type();</pre>
<p>
</p>
</li>
</ul></div>
<p>
</p>
</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>
</div></td>
</tr></table>
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