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<div class="refentry">
<a name="boost.proto.context.default_eval"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Struct template default_eval</span></h2>
<p>boost::proto::context::default_eval —
A BinaryFunction that accepts a Proto expression and a context, evaluates
each child expression with the context, and combines the result using the
standard C++ meaning for the operator represented by the current expression
node.
</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.context.default_hpp" title="Header <boost/proto/context/default.hpp>">boost/proto/context/default.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> Context<span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="default_eval.html" title="Struct template default_eval">default_eval</a> <span class="special">{</span>
<span class="comment">// <a class="link" href="default_eval.html#boost.proto.context.default_evaltypes">types</a></span>
<span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">::</span><span class="identifier">tag_type</span> <a name="boost.proto.context.default_eval.Tag"></a><span class="identifier">Tag</span><span class="special">;</span> <span class="comment">// For exposition only</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="default_eval.html#boost.proto.context.default_eval.result_type"><span class="identifier">result_type</span></a><span class="special">;</span>
<span class="comment">// <a class="link" href="default_eval.html#idm45506983453520-bb">public member functions</a></span>
<span class="identifier">result_type</span> <a class="link" href="default_eval.html#idm45506983452960-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">Expr</span> <span class="special">&</span><span class="special">,</span> <span class="identifier">Context</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="comment">// public data members</span>
<span class="keyword">static</span> <span class="identifier">Expr</span> <span class="special">&</span> <span class="identifier">s_expr</span><span class="special">;</span> <span class="comment">// For exposition only</span>
<span class="keyword">static</span> <span class="identifier">Context</span> <span class="special">&</span> <span class="identifier">s_context</span><span class="special">;</span> <span class="comment">// For exposition only</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm45555168441648"></a><h2>Description</h2>
<p>
Let <code class="computeroutput"><code class="computeroutput">OP</code></code> be the C++ operator
corresponding to <code class="computeroutput">Expr::proto_tag</code>. (For example, if
<code class="computeroutput">Tag</code> is <code class="computeroutput">
<a class="link" href="../tag/plus.html" title="Struct plus">proto::tag::plus</a></code>, let <code class="computeroutput">
<code class="computeroutput">OP</code></code> be <code class="computeroutput">+</code>.)
</p>
<p>
The behavior of this class is specified in terms of the C++0x <code class="computeroutput">decltype</code>
keyword. In systems where this keyword is not available, Proto uses the Boost.Typeof library to
approximate the behavior.
</p>
<div class="refsect2">
<a name="idm45555168433536"></a><h3>
<a name="boost.proto.context.default_evaltypes"></a><code class="computeroutput">default_eval</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.context.default_eval.result_type"></a><span class="identifier">result_type</span><span class="special">;</span></p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> corresponds to a unary prefix operator,
then the result type is
</p>
<pre class="programlisting"><span class="keyword">decltype</span><span class="special">(</span>
<span class="identifier">OP</span> <a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_idm45506990961392.html" title="Function child">proto::child</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span>
<span class="special">)</span></pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> corresponds to a unary postfix operator,
then the result type is
</p>
<pre class="programlisting"><span class="keyword">decltype</span><span class="special">(</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_idm45506990961392.html" title="Function child">proto::child</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="identifier">OP</span>
<span class="special">)</span></pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> corresponds to a binary infix operator,
then the result type is
</p>
<pre class="programlisting"><span class="keyword">decltype</span><span class="special">(</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../left_idm45506990901376.html" title="Function left">proto::left</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="identifier">OP</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../right_idm45506990886896.html" title="Function right">proto::right</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span>
<span class="special">)</span></pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> is <code class="computeroutput">
<a class="link" href="../tag/subscript.html" title="Struct subscript">proto::tag::subscript</a>
</code>,
then the result type is
</p>
<pre class="programlisting"><span class="keyword">decltype</span><span class="special">(</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../left_idm45506990901376.html" title="Function left">proto::left</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">[</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../right_idm45506990886896.html" title="Function right">proto::right</a><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">]</span>
<span class="special">)</span></pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> is <code class="computeroutput">
<a class="link" href="../tag/if_else_.html" title="Struct if_else_">proto::tag::if_else_</a>
</code>,
then the result type is
</p>
<pre class="programlisting"><span class="keyword">decltype</span><span class="special">(</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a><span class="special"><</span><span class="number">0</span><span class="special">></span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">?</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a><span class="special"><</span><span class="number">1</span><span class="special">></span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">:</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a><span class="special"><</span><span class="number">2</span><span class="special">></span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span>
<span class="special">)</span></pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> is <code class="computeroutput">
<a class="link" href="../tag/function.html" title="Struct function">proto::tag::function</a>
</code>,
then the result type is
</p>
<pre class="programlisting"><span class="keyword">decltype</span><span class="special">(</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a><span class="special"><</span><span class="number">0</span><span class="special">></span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">(</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a><span class="special"><</span><span class="number">1</span><span class="special">></span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span><span class="special">,</span>
<span class="special">...</span>
<a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a><span class="special">(</span><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a><span class="special"><</span><span class="identifier">N</span><span class="special">></span><span class="special">(</span><span class="identifier">s_expr</span><span class="special">)</span><span class="special">,</span> <span class="identifier">s_context</span><span class="special">)</span> <span class="special">)</span>
<span class="special">)</span></pre>
<p>
</p>
</li>
</ul></div>
</li></ol></div>
</div>
<div class="refsect2">
<a name="idm45555168316400"></a><h3>
<a name="idm45506983453520-bb"></a><code class="computeroutput">default_eval</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="idm45506983452960-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">Expr</span> <span class="special">&</span> expr<span class="special">,</span> <span class="identifier">Context</span> <span class="special">&</span> context<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> corresponds to a unary prefix operator,
then return
</p>
<pre class="programlisting">OP <code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_idm45506990961392.html" title="Function child">proto::child</a></code>(expr), context)</pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> corresponds to a unary postfix operator,
then return
</p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_idm45506990961392.html" title="Function child">proto::child</a></code>(expr), context) OP</pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> corresponds to a binary infix operator,
then return
</p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../left_idm45506990901376.html" title="Function left">proto::left</a></code>(expr), context) OP
<code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../right_idm45506990886896.html" title="Function right">proto::right</a></code>(expr), context)</pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> is <code class="computeroutput">
<code class="computeroutput"><a class="link" href="../tag/subscript.html" title="Struct subscript">proto::tag::subscript</a></code>
</code>,
then return
</p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../left_idm45506990901376.html" title="Function left">proto::left</a></code>(expr), context) [
<code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../right_idm45506990886896.html" title="Function right">proto::right</a></code>(expr), context) ]</pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> is <code class="computeroutput">
<code class="computeroutput"><a class="link" href="../tag/if_else_.html" title="Struct if_else_">proto::tag::if_else_</a></code>
</code>,
then return
</p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a></code><0>(expr), context) ?
<code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a></code><1>(expr), context) :
<code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a></code><2>(expr), context)</pre>
<p>
</p>
</li>
<li class="listitem">
<p>
If <code class="computeroutput">Tag</code> is <code class="computeroutput">
<code class="computeroutput"><a class="link" href="../tag/function.html" title="Struct function">proto::tag::function</a></code>
</code>,
then return
</p>
<pre class="programlisting"><code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a></code><0>(expr), context) (
<code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a></code><1>(expr), context),
...
<code class="computeroutput"><a class="link" href="../eval_idm45506996501744.html" title="Function eval">proto::eval</a></code>(<code class="computeroutput"><a class="link" href="../child_c_idm45506990932896.html" title="Function child_c">proto::child_c</a></code><N>(expr), context) )</pre>
<p>
</p>
</li>
</ul></div>
<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">context</code></span></p></td>
<td><p>The evaluation context </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">expr</code></span></p></td>
<td><p>The current expression </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>
</div></td>
</tr></table>
<hr>
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