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| <div class="refentry"> |
| <a name="boost.variant"></a><div class="titlepage"></div> |
| <div class="refnamediv"> |
| <h2><span class="refentrytitle">Class template variant</span></h2> |
| <p>boost::variant — Safe, generic, stack-based discriminated union container.</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="../variant/reference.html#header.boost.variant.variant_hpp" title="Header <boost/variant/variant.hpp>">boost/variant/variant.hpp</a>> |
| |
| </span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T1<span class="special">,</span> <span class="keyword">typename</span> T2 <span class="special">=</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> |
| <span class="keyword">typename</span> TN <span class="special">=</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span><span class="special">></span> |
| <span class="keyword">class</span> <a class="link" href="variant.html" title="Class template variant">variant</a> <span class="special">{</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="comment">// types</span> |
| <span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <a name="boost.variant.types"></a><span class="identifier">types</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="variant.html#boost.variantconstruct-copy-destruct">construct/copy/destruct</a></span> |
| <a class="link" href="variant.html#id648130-bb"><span class="identifier">variant</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> |
| <a class="link" href="variant.html#id1478186-bb"><span class="identifier">variant</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <a class="link" href="variant.html#id459933-bb"><span class="identifier">variant</span></a><span class="special">(</span><span class="identifier">T</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <a class="link" href="variant.html#id635781-bb"><span class="identifier">variant</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U1<span class="special">,</span> <span class="keyword">typename</span> U2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> UN<span class="special">></span> |
| <a class="link" href="variant.html#id632990-bb"><span class="identifier">variant</span></a><span class="special">(</span><span class="identifier">variant</span><span class="special"><</span><span class="identifier">U1</span><span class="special">,</span> <span class="identifier">U2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">UN</span><span class="special">></span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U1<span class="special">,</span> <span class="keyword">typename</span> U2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> UN<span class="special">></span> |
| <a class="link" href="variant.html#id476388-bb"><span class="identifier">variant</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span><span class="special"><</span><span class="identifier">U1</span><span class="special">,</span> <span class="identifier">U2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">UN</span><span class="special">></span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <a class="link" href="variant.html#id435438-bb"><span class="special">~</span><span class="identifier">variant</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="variant.html#id1344014-bb">modifiers</a></span> |
| <span class="keyword">void</span> <a class="link" href="variant.html#id1344017-bb"><span class="identifier">swap</span></a><span class="special">(</span><span class="identifier">variant</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="identifier">variant</span> <span class="special">&</span> <a class="link" href="variant.html#id1382746-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="identifier">variant</span> <span class="special">&</span> <a class="link" href="variant.html#id460433-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="variant.html#id1505403-bb">queries</a></span> |
| <span class="keyword">int</span> <a class="link" href="variant.html#id1505407-bb"><span class="identifier">which</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">bool</span> <a class="link" href="variant.html#id1486747-bb"><span class="identifier">empty</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span> <span class="special">&</span> <a class="link" href="variant.html#id465357-bb"><span class="identifier">type</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| |
| <span class="comment">// <a class="link" href="variant.html#id1486865-bb">relational</a></span> |
| <span class="keyword">bool</span> <a class="link" href="variant.html#id1504311-bb"><span class="keyword">operator</span><span class="special">==</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U<span class="special">></span> <span class="keyword">void</span> <a class="link" href="variant.html#id342749-bb"><span class="keyword">operator</span><span class="special">==</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">U</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">bool</span> <a class="link" href="variant.html#id1371063-bb"><span class="keyword">operator</span><span class="special"><</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U<span class="special">></span> <span class="keyword">void</span> <a class="link" href="variant.html#id1503788-bb"><span class="keyword">operator</span><span class="special"><</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">U</span> <span class="special">&</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="id3077259"></a><h2>Description</h2> |
| <p>The <code class="computeroutput">variant</code> class template (inspired by Andrei |
| Alexandrescu's class of the same name |
| [<a class="link" href="../variant/refs.html#variant.refs.ale01a">Ale01A</a>]) is an efficient, |
| <a class="link" href="../variant/tutorial.html#variant.tutorial.recursive" title="Recursive variant types">recursive-capable</a>, |
| bounded discriminated union value type capable of containing any value |
| type (either POD or non-POD). It supports construction from any type |
| convertible to one of its bounded types or from a source |
| <code class="computeroutput">variant</code> whose bounded types are each convertible to one |
| of the destination <code class="computeroutput">variant</code>'s bounded types. As well, |
| through <code class="computeroutput"><a class="link" href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code>, |
| <code class="computeroutput">variant</code> supports compile-time checked, type-safe |
| visitation; and through <code class="computeroutput"><a class="link" href="get_id1380826.html" title="Function get">get</a></code>, |
| <code class="computeroutput">variant</code> supports run-time checked, type-safe value |
| retrieval.</p> |
| <p><span class="bold"><strong>Notes</strong></span>:</p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem">The bounded types of the <code class="computeroutput">variant</code> are exposed |
| via the nested typedef <code class="computeroutput">types</code>, which is an |
| <a href="../../../libs/mpl/index.html" target="_top">MPL</a>-compatible Sequence containing the |
| set of types that must be handled by any |
| <a class="link" href="../variant/reference.html#variant.concepts.static-visitor" title="StaticVisitor">visitor</a> to |
| the <code class="computeroutput">variant</code>.</li> |
| <li class="listitem">All members of <code class="computeroutput">variant</code> satisfy at least the |
| basic guarantee of exception-safety. That is, all operations on |
| a <code class="computeroutput">variant</code> remain defined even after previous |
| operations have failed.</li> |
| <li class="listitem">Each type specified as a template argument to |
| <code class="computeroutput">variant</code> must meet the requirements of the |
| <span class="emphasis"><em><a class="link" href="../variant/reference.html#variant.concepts.bounded-type" title="BoundedType">BoundedType</a></em></span> |
| concept.</li> |
| <li class="listitem">Each type specified as a template argument to |
| <code class="computeroutput">variant</code> must be distinct after removal of qualifiers. |
| Thus, for instance, both <code class="computeroutput">variant<int, int></code> and |
| <code class="computeroutput">variant<int, const int></code> have undefined |
| behavior.</li> |
| <li class="listitem">Conforming implementations of <code class="computeroutput">variant</code> must |
| allow at least ten types as template arguments. The exact number |
| of allowed arguments is exposed by the preprocessor macro |
| <code class="computeroutput"><a class="link" href="../BOOST_VARIANT_LIMIT_TYPES.html" title="Macro BOOST_VARIANT_LIMIT_TYPES">BOOST_VARIANT_LIMIT_TYPES</a></code>. |
| (See <code class="computeroutput"><a class="link" href="make_variant_over.html" title="Class template make_variant_over">make_variant_over</a></code> for a |
| means to specify the bounded types of a <code class="computeroutput">variant</code> by |
| the elements of an <a href="../../../libs/mpl/index.html" target="_top">MPL</a> or compatible |
| Sequence, thus overcoming this limitation.)</li> |
| </ul></div> |
| <div class="refsect2"> |
| <a name="id3077503"></a><h3> |
| <a name="boost.variantconstruct-copy-destruct"></a><code class="computeroutput">variant</code> |
| public |
| construct/copy/destruct</h3> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| <pre class="literallayout"><a name="id648130-bb"></a><span class="identifier">variant</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Requires:</span></p></td> |
| <td>The first bounded type of the <code class="computeroutput">variant</code> (i.e., |
| <code class="computeroutput">T1</code>) must fulfill the requirements of the |
| <span class="emphasis"><em>DefaultConstructible</em></span> [20.1.4] |
| concept.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Postconditions:</span></p></td> |
| <td>Content of <code class="computeroutput">*this</code> is the default value of the |
| first bounded type (i.e, <code class="computeroutput">T1</code>).</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>May fail with any exceptions arising from the default |
| constructor of <code class="computeroutput">T1</code>.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><a name="id1478186-bb"></a><span class="identifier">variant</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span> <span class="special">&</span> other<span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Postconditions:</span></p></td> |
| <td>Content of <code class="computeroutput">*this</code> is a copy of the content of |
| <code class="computeroutput">other</code>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>May fail with any exceptions arising from the |
| copy constructor of <code class="computeroutput">other</code>'s contained type.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <a name="id459933-bb"></a><span class="identifier">variant</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Requires:</span></p></td> |
| <td> |
| <code class="computeroutput">T</code> must be unambiguously convertible to one of |
| the bounded types (i.e., <code class="computeroutput">T1</code>, <code class="computeroutput">T2</code>, |
| etc.).</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Postconditions:</span></p></td> |
| <td>Content of <code class="computeroutput">*this</code> is the best conversion of |
| <code class="computeroutput">operand</code> to one of the bounded types, as determined |
| by standard overload resolution rules.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>May fail with any exceptions arising from the conversion of |
| <code class="computeroutput">operand</code> to one of the bounded types.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <a name="id635781-bb"></a><span class="identifier">variant</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody><tr> |
| <td><p><span class="term">Notes:</span></p></td> |
| <td>Same semantics as previous constructor, but allows |
| construction from temporaries.</td> |
| </tr></tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U1<span class="special">,</span> <span class="keyword">typename</span> U2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> UN<span class="special">></span> |
| <a name="id632990-bb"></a><span class="identifier">variant</span><span class="special">(</span><span class="identifier">variant</span><span class="special"><</span><span class="identifier">U1</span><span class="special">,</span> <span class="identifier">U2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">UN</span><span class="special">></span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Requires:</span></p></td> |
| <td> |
| <span class="emphasis"><em>Every</em></span> one of <code class="computeroutput">U1</code>, |
| <code class="computeroutput">U2</code>, ..., <code class="computeroutput">UN</code> must have an unambiguous |
| conversion to one of the bounded types (i.e., <code class="computeroutput">T1</code>, |
| <code class="computeroutput">T2</code>, ..., <code class="computeroutput">TN</code>).</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Postconditions:</span></p></td> |
| <td>If <code class="computeroutput">variant<U1, U2, ..., UN></code> is itself |
| one of the bounded types, then content of <code class="computeroutput">*this</code> is a |
| copy of <code class="computeroutput">operand</code>. Otherwise, content of |
| <code class="computeroutput">*this</code> is the best conversion of the content of |
| <code class="computeroutput">operand</code> to one of the bounded types, as determined |
| by standard overload resolution rules.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>If <code class="computeroutput">variant<U1, U2, ..., UN></code> is itself |
| one of the bounded types, then may fail with any exceptions arising |
| from the copy constructor of |
| <code class="computeroutput">variant<U1, U2, ..., UN></code>. Otherwise, may fail |
| with any exceptions arising from the conversion of the content of |
| <code class="computeroutput">operand</code> to one of the bounded types.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U1<span class="special">,</span> <span class="keyword">typename</span> U2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> UN<span class="special">></span> |
| <a name="id476388-bb"></a><span class="identifier">variant</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span><span class="special"><</span><span class="identifier">U1</span><span class="special">,</span> <span class="identifier">U2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">UN</span><span class="special">></span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody><tr> |
| <td><p><span class="term">Notes:</span></p></td> |
| <td>Same semantics as previous constructor, but allows |
| construction from temporaries.</td> |
| </tr></tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><a name="id435438-bb"></a><span class="special">~</span><span class="identifier">variant</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Effects:</span></p></td> |
| <td>Destroys the content of <code class="computeroutput">*this</code>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>Will not throw.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| </ol></div> |
| </div> |
| <div class="refsect2"> |
| <a name="id3078369"></a><h3> |
| <a name="id1344014-bb"></a><code class="computeroutput">variant</code> modifiers</h3> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">void</span> <a name="id1344017-bb"></a><span class="identifier">swap</span><span class="special">(</span><span class="identifier">variant</span> <span class="special">&</span> other<span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Requires:</span></p></td> |
| <td>Every bounded type must fulfill the requirements of the |
| <a class="link" href="../Assignable.html" title="Concept Assignable">Assignable</a> |
| concept.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Effects:</span></p></td> |
| <td>Interchanges the content of <code class="computeroutput">*this</code> and |
| <code class="computeroutput">other</code>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>If the contained type of <code class="computeroutput">other</code> is the same as |
| the contained type of <code class="computeroutput">*this</code>, then may fail with any |
| exceptions arising from the <code class="computeroutput">swap</code> of the contents of |
| <code class="computeroutput">*this</code> and <code class="computeroutput">other</code>. Otherwise, may fail |
| with any exceptions arising from either of the copy constructors |
| of the contained types. Also, in the event of insufficient |
| memory, may fail with <code class="computeroutput">std::bad_alloc</code> |
| (<a class="link" href="../variant/design.html#variant.design.never-empty.problem" title="The Implementation Problem">why?</a>).</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="identifier">variant</span> <span class="special">&</span> <a name="id1382746-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span> <span class="special">&</span> rhs<span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Requires:</span></p></td> |
| <td>Every bounded type must fulfill the requirements of the |
| <a class="link" href="../Assignable.html" title="Concept Assignable">Assignable</a> |
| concept.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Effects:</span></p></td> |
| <td>If the contained type of <code class="computeroutput">rhs</code> is the same as |
| the contained type of <code class="computeroutput">*this</code>, then assigns the |
| content of <code class="computeroutput">rhs</code> into the content of |
| <code class="computeroutput">*this</code>. Otherwise, makes the content of |
| <code class="computeroutput">*this</code> a copy of the content of <code class="computeroutput">rhs</code>, |
| destroying the previous content of <code class="computeroutput">*this</code>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>If the contained type of <code class="computeroutput">rhs</code> is the same as |
| the contained type of <code class="computeroutput">*this</code>, then may fail with any |
| exceptions arising from the assignment of the content of |
| <code class="computeroutput">rhs</code> into the content <code class="computeroutput">*this</code>. Otherwise, |
| may fail with any exceptions arising from the copy constructor |
| of the contained type of <code class="computeroutput">rhs</code>. Also, in the event of |
| insufficient memory, may fail with <code class="computeroutput">std::bad_alloc</code> |
| (<a class="link" href="../variant/design.html#variant.design.never-empty.problem" title="The Implementation Problem">why?</a>).</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="identifier">variant</span> <span class="special">&</span> <a name="id460433-bb"></a><span class="keyword">operator</span><span class="special">=</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> rhs<span class="special">)</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Requires:</span></p></td> |
| <td><div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <code class="computeroutput">T</code> must be unambiguously convertible to |
| one of the bounded types (i.e., <code class="computeroutput">T1</code>, |
| <code class="computeroutput">T2</code>, etc.).</li> |
| <li class="listitem">Every bounded type must fulfill the requirements of the |
| <a class="link" href="../Assignable.html" title="Concept Assignable">Assignable</a> |
| concept.</li> |
| </ul></div></td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Effects:</span></p></td> |
| <td>If the contained type of <code class="computeroutput">*this</code> is |
| <code class="computeroutput">T</code>, then assigns <code class="computeroutput">rhs</code> into the content |
| of <code class="computeroutput">*this</code>. Otherwise, makes the content of |
| <code class="computeroutput">*this</code> the best conversion of <code class="computeroutput">rhs</code> to |
| one of the bounded types, as determined by standard overload |
| resolution rules, destroying the previous content of |
| <code class="computeroutput">*this</code>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>If the contained type of <code class="computeroutput">*this</code> is |
| <code class="computeroutput">T</code>, then may fail with any exceptions arising from |
| the assignment of <code class="computeroutput">rhs</code> into the content |
| <code class="computeroutput">*this</code>. Otherwise, may fail with any exceptions |
| arising from the conversion of <code class="computeroutput">rhs</code> to one of the |
| bounded types. Also, in the event of insufficient memory, may |
| fail with <code class="computeroutput">std::bad_alloc</code> |
| (<a class="link" href="../variant/design.html#variant.design.never-empty.problem" title="The Implementation Problem">why?</a>).</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| </ol></div> |
| </div> |
| <div class="refsect2"> |
| <a name="id3078949"></a><h3> |
| <a name="id1505403-bb"></a><code class="computeroutput">variant</code> queries</h3> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">int</span> <a name="id1505407-bb"></a><span class="identifier">which</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Returns:</span></p></td> |
| <td>The zero-based index into the set of bounded types |
| of the contained type of <code class="computeroutput">*this</code>. (For instance, if |
| called on a <code class="computeroutput">variant<int, std::string></code> object |
| containing a <code class="computeroutput">std::string</code>, <code class="computeroutput">which()</code> |
| would return <code class="computeroutput">1</code>.)</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>Will not throw.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">bool</span> <a name="id1486747-bb"></a><span class="identifier">empty</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Returns:</span></p></td> |
| <td> |
| <code class="computeroutput">false</code>: <code class="computeroutput">variant</code> always contains |
| exactly one of its bounded types. (See |
| <a class="xref" href="../variant/design.html#variant.design.never-empty" title='"Never-Empty" Guarantee'>the section called “"Never-Empty" Guarantee”</a> |
| for more information.)</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Rationale:</span></p></td> |
| <td>Facilitates generic compatibility with |
| <a class="link" href="any.html" title="Class any">boost::any</a>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>Will not throw.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span> <span class="special">&</span> <a name="id465357-bb"></a><span class="identifier">type</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Returns:</span></p></td> |
| <td> |
| <code class="computeroutput">typeid(x)</code>, where <code class="computeroutput">x</code> is the the |
| content of <code class="computeroutput">*this</code>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>Will not throw.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Notes:</span></p></td> |
| <td>Not available when <code class="computeroutput">BOOST_NO_TYPEID</code> is |
| defined.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| </ol></div> |
| </div> |
| <div class="refsect2"> |
| <a name="id3079256"></a><h3> |
| <a name="id1486865-bb"></a><code class="computeroutput">variant</code> relational</h3> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| <pre class="literallayout"><a name="id423348-bb"></a><span class="keyword">bool</span> <a name="id1504311-bb"></a><span class="keyword">operator</span><span class="special">==</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span> <span class="special">&</span> rhs<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U<span class="special">></span> <span class="keyword">void</span> <a name="id342749-bb"></a><span class="keyword">operator</span><span class="special">==</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">U</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>Equality comparison.<div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Notes:</span></p></td> |
| <td>The overload returning <code class="computeroutput">void</code> exists only to |
| prohibit implicit conversion of the operator's right-hand side |
| to <code class="computeroutput">variant</code>; thus, its use will (purposefully) |
| result in a compile-time error.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Requires:</span></p></td> |
| <td>Every bounded type of the <code class="computeroutput">variant</code> must |
| fulfill the requirements of the |
| <a class="link" href="../EqualityComparable.html" title="Concept EqualityComparable">EqualityComparable</a> |
| concept.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Returns:</span></p></td> |
| <td> |
| <code class="computeroutput">true</code> iff <code class="computeroutput">which() == rhs.which()</code> |
| <span class="emphasis"><em>and</em></span> |
| <code class="computeroutput">content_this == content_rhs</code>, where |
| <code class="computeroutput">content_this</code> is the content of <code class="computeroutput">*this</code> |
| and <code class="computeroutput">content_rhs</code> is the content of |
| <code class="computeroutput">rhs</code>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>If <code class="computeroutput">which() == rhs.which()</code> then may fail with |
| any exceptions arising from <code class="computeroutput">operator==(T,T)</code>, where |
| <code class="computeroutput">T</code> is the contained type of |
| <code class="computeroutput">*this</code>.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </li> |
| <li class="listitem"> |
| <pre class="literallayout"><a name="id704845-bb"></a><span class="keyword">bool</span> <a name="id1371063-bb"></a><span class="keyword">operator</span><span class="special"><</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">variant</span> <span class="special">&</span> rhs<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U<span class="special">></span> <span class="keyword">void</span> <a name="id1503788-bb"></a><span class="keyword">operator</span><span class="special"><</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">U</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>LessThan comparison.<div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Notes:</span></p></td> |
| <td>The overload returning <code class="computeroutput">void</code> exists only to |
| prohibit implicit conversion of the operator's right-hand side |
| to <code class="computeroutput">variant</code>; thus, its use will (purposefully) |
| result in a compile-time error.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Requires:</span></p></td> |
| <td>Every bounded type of the <code class="computeroutput">variant</code> must |
| fulfill the requirements of the |
| <a class="link" href="../LessThanComparable.html" title="Concept LessThanComparable">LessThanComparable</a> |
| concept.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Returns:</span></p></td> |
| <td>If <code class="computeroutput">which() == rhs.which()</code> then: |
| <code class="computeroutput">content_this < content_rhs</code>, where |
| <code class="computeroutput">content_this</code> is the content of <code class="computeroutput">*this</code> |
| and <code class="computeroutput">content_rhs</code> is the content of <code class="computeroutput">rhs</code>. |
| Otherwise: <code class="computeroutput">which() < rhs.which()</code>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>If <code class="computeroutput">which() == rhs.which()</code> then may fail with |
| any exceptions arising from <code class="computeroutput">operator<(T,T)</code>, |
| where <code class="computeroutput">T</code> is the contained type of |
| <code class="computeroutput">*this</code>.</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 © 2002, 2003 Eric Friedman, Itay Maman<p>Distributed under the Boost Software License, Version 1.0. |
| (See accompanying file <code class="filename">LICENSE_1_0.txt</code> 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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