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<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.advanced.customize.store_value.push_back"></a><a class="link" href="push_back.html" title="Store a Parsed Attribute Value into a Container (Qi)">
Store a Parsed Attribute Value into a Container (Qi)</a>
</h5></div></div></div>
<a name="spirit.advanced.customize.store_value.push_back.push_back_container"></a><h6>
<a name="id1216238"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.push_back_container">push_back_container</a>
</h6>
<p>
The template <code class="computeroutput"><span class="identifier">push_back_container</span></code>
is a type used as an attribute customization point. It is invoked by
the <span class="emphasis"><em>Qi</em></span> repetitive parsers (<a class="link" href="../../../qi/reference/operator/kleene.html" title="Kleene (*a)">Kleene</a>,
<a class="link" href="../../../qi/reference/operator/plus.html" title="Plus (+a)">Plus</a>, <a class="link" href="../../../qi/reference/operator/list.html" title="List (a % b)">List</a>, and <a class="link" href="../../../qi/reference/directive/repeat.html" title="Repetition (repeat[])">Repeat</a>)
to store a parsed attribute value into a container.
</p>
<a name="spirit.advanced.customize.store_value.push_back.module_headers"></a><h6>
<a name="id1216288"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.module_headers">Module
Headers</a>
</h6>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">home</span><span class="special">/</span><span class="identifier">support</span><span class="special">/</span><span class="identifier">container</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<p>
Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
This header file does not need to be included directly by any user
program as it is normally included by other Spirit header files relying
on its content.
</p></td></tr>
</table></div>
<a name="spirit.advanced.customize.store_value.push_back.namespace"></a><h6>
<a name="id1216378"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.namespace">Namespace</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
<p>
Name
</p>
</th></tr></thead>
<tbody><tr><td>
<p>
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">traits</span></code>
</p>
</td></tr></tbody>
</table></div>
<a name="spirit.advanced.customize.store_value.push_back.synopsis"></a><h6>
<a name="id1216456"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.synopsis">Synopsis</a>
</h6>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Attrib</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Enable</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">push_back_container</span>
<span class="special">{</span>
<span class="keyword">static</span> <span class="keyword">bool</span> <span class="identifier">call</span><span class="special">(</span><span class="identifier">Container</span><span class="special">&</span> <span class="identifier">c</span><span class="special">,</span> <span class="identifier">Attrib</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span>
<span class="special">};</span>
</pre>
<a name="spirit.advanced.customize.store_value.push_back.template_parameters"></a><h6>
<a name="id1216597"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.template_parameters">Template
parameters</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Description
</p>
</th>
<th>
<p>
Default
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">Container</span></code>
</p>
</td>
<td>
<p>
The type, <code class="computeroutput"><span class="identifier">Container</span></code>
needs to be tested whether it has to be treated as a container
</p>
</td>
<td>
<p>
none
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">Attrib</span></code>
</p>
</td>
<td>
<p>
The type, <code class="computeroutput"><span class="identifier">Attrib</span></code>
is the one returned from the customization point <a class="link" href="container_value.html" title="Determine the Type to be Stored in a Container (Qi)"><code class="computeroutput"><span class="identifier">container_value</span></code></a> and
represents the attribute value to be stored in the container
of type <code class="computeroutput"><span class="identifier">Container</span></code>.
</p>
</td>
<td>
<p>
none
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">Enable</span></code>
</p>
</td>
<td>
<p>
Helper template parameter usable to selectively enable or disable
certain specializations of <code class="computeroutput"><span class="identifier">push_back_container</span></code>
utilizing SFINAE (i.e. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">enable_if</span></code>
or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">disable_if</span></code>).
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="spirit.advanced.customize.store_value.push_back.notation"></a><h6>
<a name="id1217510"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.notation">Notation</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term"><code class="computeroutput"><span class="identifier">C</span></code></span></dt>
<dd><p>
A type to be used as a container to store attribute values in.
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">c</span></code></span></dt>
<dd>
<p>
A container instance of type <code class="computeroutput"><span class="identifier">C</span></code>.
</p>
<p>
[<code class="computeroutput"><span class="identifier">Attrib</span></code>
</p>
<p>
A type to be used as a container to store attribute values in.
</p>
</dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">attr</span></code></span></dt>
<dd><p>
A attribute instance of type <code class="computeroutput"><span class="identifier">Attrib</span></code>.
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">T1</span></code>, <code class="computeroutput"><span class="identifier">T2</span></code>, ...</span></dt>
<dd><p>
Arbitrary types
</p></dd>
</dl>
</div>
<a name="spirit.advanced.customize.store_value.push_back.expression_semantics"></a><h6>
<a name="id1217652"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.expression_semantics">Expression
Semantics</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">push_back_container</span><span class="special"><</span><span class="identifier">C</span><span class="special">,</span> <span class="identifier">Attrib</span><span class="special">>::</span><span class="identifier">call</span><span class="special">(</span><span class="identifier">c</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">)</span></pre>
<p>
</p>
</td>
<td>
<p>
Static function that is invoked whenever an attribute value,
<code class="computeroutput"><span class="identifier">attr</span></code> needs
to be stored into the container instance <code class="computeroutput"><span class="identifier">c</span></code>.
This function should return <code class="computeroutput"><span class="keyword">true</span></code>
on success and <code class="computeroutput"><span class="keyword">false</span></code>
otherwise. Returning <code class="computeroutput"><span class="keyword">false</span></code>
causes the corresponding parser to fail.
</p>
</td>
</tr></tbody>
</table></div>
<a name="spirit.advanced.customize.store_value.push_back.predefined_specializations"></a><h6>
<a name="id1217804"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.predefined_specializations">Predefined
Specializations</a>
</h6>
<p>
<a href="http://boost-spirit.com" target="_top">Spirit</a> predefines specializations
of this customization point for several types. The following table lists
those types together with the types exposed and the corresponding semantics:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Template Parameters
</p>
</th>
<th>
<p>
Value
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">C</span></code>, <code class="computeroutput"><span class="identifier">Attrib</span></code>
</p>
</td>
<td>
<p>
Store the provided attribute instance <code class="computeroutput"><span class="identifier">attr</span></code>
into the given container <code class="computeroutput"><span class="identifier">c</span></code>
using the function call <code class="computeroutput"><span class="identifier">c</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">c</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">attr</span><span class="special">)</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span></code>,
<code class="computeroutput"><span class="identifier">Attrib</span></code>
</p>
</td>
<td>
<p>
If the provided instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><></span></code> is not initialized,
invoke the appropriate initialization and afterwards apply
the customization point <code class="computeroutput"><span class="identifier">push_back_container</span><span class="special"><</span><span class="identifier">C</span><span class="special">,</span> <span class="identifier">Attrib</span><span class="special">></span></code>, treating the instance
held by the optional (of type <code class="computeroutput"><span class="identifier">C</span></code>)
as the container to store the attribute in.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special"><</span><span class="identifier">T1</span><span class="special">,</span>
<span class="identifier">T2</span><span class="special">,</span>
<span class="special">...></span></code>, <code class="computeroutput"><span class="identifier">Attrib</span></code>
</p>
</td>
<td>
<p>
If the instance of the variant currently holds a value with
a type, <code class="computeroutput"><span class="identifier">TN</span></code>,
for which <code class="computeroutput"><span class="identifier">is_container</span><span class="special"><</span><span class="identifier">TN</span><span class="special">>::</span><span class="identifier">type</span></code>
evaluates to <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>,
this customization point specialization will apply <code class="computeroutput"><span class="identifier">push_back_container</span><span class="special"><</span><span class="identifier">TN</span><span class="special">,</span>
<span class="identifier">Attrib</span><span class="special">></span></code>,
treating the instance held by the variant (of type <code class="computeroutput"><span class="identifier">TN</span></code>) as the container to store
the attribute in. Otherwise it will raise an assertion.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">unused_type</span></code>
</p>
</td>
<td>
<p>
Do nothing.
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="spirit.advanced.customize.store_value.push_back.when_to_implement"></a><h6>
<a name="id1218218"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.when_to_implement">When
to Implement</a>
</h6>
<p>
The customization point <code class="computeroutput"><span class="identifier">push_back_container</span></code>
needs to be implemented for a specific type whenever this type is to
be used as an attribute in place of a STL container. It is applicable
for parsers (<span class="emphasis"><em>Spirit.Qi</em></span>) only. As a rule of thumb:
it has to be implemented whenever a certain type is to be passed as an
attribute to a parser normally exposing a STL container and if the type
does not expose the interface of a STL container (i.e. no function being
equivalent to <code class="computeroutput"><span class="identifier">c</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">c</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">attr</span><span class="special">)</span></code>.
These components have an attribute propagation rule in the form:
</p>
<pre class="programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--></span> <span class="identifier">Op</span><span class="special">(</span><span class="identifier">a</span><span class="special">):</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span>
</pre>
<p>
where <code class="computeroutput"><span class="identifier">Op</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code>
stands for any meaningful operation on the component <code class="computeroutput"><span class="identifier">a</span></code>.
</p>
<a name="spirit.advanced.customize.store_value.push_back.related_attribute_customization_points"></a><h6>
<a name="id1218368"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.related_attribute_customization_points">Related
Attribute Customization Points</a>
</h6>
<p>
If this customization point is implemented, the following other customization
points might need to be implemented as well.
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
When to implement
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="container_value.html" title="Determine the Type to be Stored in a Container (Qi)"><code class="computeroutput"><span class="identifier">container_value</span></code></a>
</p>
</td>
<td>
<p>
Qi: <a class="link" href="../../../qi/reference/operator/list.html" title="List (a % b)">List</a>,
<a class="link" href="../../../qi/reference/operator/kleene.html" title="Kleene (*a)">Kleene</a>,
<a class="link" href="../../../qi/reference/operator/plus.html" title="Plus (+a)">Plus</a>,
<a class="link" href="../../../qi/reference/directive/repeat.html" title="Repetition (repeat[])">Repeat</a>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="../clear_value.html" title="Re-Initialize an Attribute Value before Parsing (Qi)"><code class="computeroutput"><span class="identifier">clear_value</span></code></a>
</p>
</td>
<td>
<p>
Qi: <a class="link" href="../../../qi/reference/operator/list.html" title="List (a % b)">List</a>,
<a class="link" href="../../../qi/reference/operator/kleene.html" title="Kleene (*a)">Kleene</a>,
<a class="link" href="../../../qi/reference/operator/plus.html" title="Plus (+a)">Plus</a>,
<a class="link" href="../../../qi/reference/directive/repeat.html" title="Repetition (repeat[])">Repeat</a>.
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="spirit.advanced.customize.store_value.push_back.example"></a><h6>
<a name="id1218514"></a>
<a class="link" href="push_back.html#spirit.advanced.customize.store_value.push_back.example">Example</a>
</h6>
<p>
Here is an example showing the default implementation of the <a class="link" href="container_value.html" title="Determine the Type to be Stored in a Container (Qi)"><code class="computeroutput"><span class="identifier">container_value</span></code></a> customization
point provided by the library:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Enable</span><span class="comment">/* = void*/</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">push_back_container</span>
<span class="special">{</span>
<span class="keyword">static</span> <span class="keyword">bool</span> <span class="identifier">call</span><span class="special">(</span><span class="identifier">Container</span><span class="special">&</span> <span class="identifier">c</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">c</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">c</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">val</span><span class="special">);</span>
<span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
This template is instantiated by the library at the appropriate places
while using the supplied container and element types as the template
arguments. The member function <code class="computeroutput"><span class="identifier">call</span><span class="special">()</span></code> will be called whenever an element
has to be added to the supplied container
</p>
<p>
The following example shows the predefined specialization for <code class="computeroutput"><span class="identifier">unused_type</span></code>:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">></span>
<span class="keyword">bool</span> <span class="identifier">push_back</span><span class="special">(</span><span class="identifier">Container</span><span class="special">&,</span> <span class="identifier">unused_type</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
which defines an empty member function <code class="computeroutput"><span class="identifier">call</span><span class="special">()</span></code>.
</p>
<p>
More examples: TBD
</p>
</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 © 2001-2010 Joel de Guzman, Hartmut Kaiser<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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