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| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.advanced.customize.store_value.container_value"></a><a class="link" href="container_value.html" title="Determine the Type to be Stored in a Container (Qi)">Determine |
| the Type to be Stored in a Container (Qi)</a> |
| </h5></div></div></div> |
| <a name="spirit.advanced.customize.store_value.container_value.container_value"></a><h6> |
| <a name="id1168902"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.container_value">container_value</a> |
| </h6> |
| <p> |
| The template <code class="computeroutput"><span class="identifier">container_value</span></code> |
| is a template meta function 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 determine |
| the type to store in a container. |
| </p> |
| <a name="spirit.advanced.customize.store_value.container_value.module_headers"></a><h6> |
| <a name="id1168949"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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.container_value.namespace"></a><h6> |
| <a name="id1169037"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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.container_value.synopsis"></a><h6> |
| <a name="id1169115"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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">Enable</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">container_value</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="special"><</span><span class="identifier">unspecified</span><span class="special">></span> <span class="identifier">type</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <a name="spirit.advanced.customize.store_value.container_value.template_parameters"></a><h6> |
| <a name="id1170989"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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> |
| is the type for which the type f the elements has to be deduced. |
| </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">container_value</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.container_value.notation"></a><h6> |
| <a name="id1171162"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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 tested whether it needs to be treated as a container. |
| </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.container_value.expression_semantics"></a><h6> |
| <a name="id1171230"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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> |
| <code class="computeroutput"><span class="identifier">container_value</span><span class="special"><</span><span class="identifier">C</span><span class="special">>::</span><span class="identifier">type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Metafunction that evaluates to the type to be stored in a given |
| container type, <code class="computeroutput"><span class="identifier">C</span></code>. |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.advanced.customize.store_value.container_value.predefined_specializations"></a><h6> |
| <a name="id1171325"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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> |
| </p> |
| </td> |
| <td> |
| <p> |
| The non-const <code class="computeroutput"><span class="identifier">value_type</span></code> |
| of the given container type, <code class="computeroutput"><span class="identifier">C</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> |
| </p> |
| </td> |
| <td> |
| <p> |
| Returns <code class="computeroutput"><span class="identifier">container_value</span><span class="special"><</span><span class="identifier">C</span><span class="special">>::</span><span class="identifier">type</span></code> |
| </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> |
| </p> |
| </td> |
| <td> |
| <p> |
| Returns <code class="computeroutput"><span class="identifier">container_value</span><span class="special"><</span><span class="identifier">TN</span><span class="special">>::</span><span class="identifier">value</span></code> |
| for the first <code class="computeroutput"><span class="identifier">TN</span></code> |
| (out of <code class="computeroutput"><span class="identifier">T1</span></code>, |
| <code class="computeroutput"><span class="identifier">T2</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>. |
| Otherwise it will return <code class="computeroutput"><span class="identifier">unused_type</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unused_type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Returns <code class="computeroutput"><span class="identifier">unused_type</span></code>. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.advanced.customize.store_value.container_value.when_to_implement"></a><h6> |
| <a name="id1171662"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.when_to_implement">When |
| to implement</a> |
| </h6> |
| <p> |
| The customization point <code class="computeroutput"><span class="identifier">is_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 embedded typedef |
| for <code class="computeroutput"><span class="identifier">value_type</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.container_value.related_attribute_customization_points"></a><h6> |
| <a name="id1171778"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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="push_back.html" title="Store a Parsed Attribute Value into a Container (Qi)"><code class="computeroutput"><span class="identifier">push_back_container</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.container_value.example"></a><h6> |
| <a name="id1171927"></a> |
| <a class="link" href="container_value.html#spirit.advanced.customize.store_value.container_value.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">Enable</span><span class="comment">/* = void*/</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">container_value</span> |
| <span class="special">:</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">remove_value_const</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">::</span><span class="identifier">value_type</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 type as the template argument. The |
| embedded <code class="computeroutput"><span class="identifier">type</span></code> is used |
| as the attribute type while parsing the elements to be store in that |
| 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">struct</span> <span class="identifier">container_value</span><span class="special"><</span><span class="identifier">unused_type</span><span class="special">></span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">unused_type</span> <span class="identifier">type</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| which defines its embedded <code class="computeroutput"><span class="identifier">type</span></code> |
| to be <code class="computeroutput"><span class="identifier">unused_type</span></code> as |
| well, this way propagating the 'don't care' attribute status to the embedded |
| parser. |
| </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> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="../store_value.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../store_value.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="push_back.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> |
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