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25<div class="refentry" lang="en">
26<a name="boost.variant"></a><div class="titlepage"></div>
27<div class="refnamediv">
28<h2><span class="refentrytitle">Class template variant</span></h2>
29<p>boost::variant &#8212; Safe, generic, stack-based discriminated union container.</p>
30</div>
31<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
32<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> T1, <span class="bold"><strong>typename</strong></span> T2 = <span class="emphasis"><em>unspecified</em></span>, ...,
33         <span class="bold"><strong>typename</strong></span> TN = <span class="emphasis"><em>unspecified</em></span>&gt; 
34<span class="bold"><strong>class</strong></span> variant {
35<span class="bold"><strong>public</strong></span>:
36  <span class="emphasis"><em>// types</em></span>
37  <span class="bold"><strong>typedef</strong></span> <span class="emphasis"><em>unspecified</em></span> types;
38
39  <span class="emphasis"><em>// <a href="variant.html#boost.variantconstruct-copy-destruct">construct/copy/destruct</a></em></span>
40  <a href="variant.html#id1602028-bb">variant</a>();
41  <a href="variant.html#id1599613-bb">variant</a>(<span class="bold"><strong>const</strong></span> variant &amp;);
42  <span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> T&gt; <a href="variant.html#id1254269-bb">variant</a>(T &amp;);
43  <span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> T&gt; <a href="variant.html#id1636459-bb">variant</a>(<span class="bold"><strong>const</strong></span> T &amp;);
44  <span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> U1, <span class="bold"><strong>typename</strong></span> U2, ..., <span class="bold"><strong>typename</strong></span> UN&gt; 
45    <a href="variant.html#id1604404-bb">variant</a>(variant&lt;U1, U2, ..., UN&gt; &amp;);
46  <span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> U1, <span class="bold"><strong>typename</strong></span> U2, ..., <span class="bold"><strong>typename</strong></span> UN&gt; 
47    <a href="variant.html#id1630438-bb">variant</a>(<span class="bold"><strong>const</strong></span> variant&lt;U1, U2, ..., UN&gt; &amp;);
48  <a href="variant.html#id1601741-bb">~variant</a>();
49
50  <span class="emphasis"><em>// <a href="variant.html#id790460-bb">modifiers</a></em></span>
51  <span class="type"><span class="bold"><strong>void</strong></span></span> <a href="variant.html#id790464-bb">swap</a>(variant &amp;);
52  <span class="type">variant &amp;</span> <a href="variant.html#id1669309-bb"><span class="bold"><strong>operator</strong></span>=</a>(<span class="bold"><strong>const</strong></span> variant &amp;);
53  <span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> T&gt; <span class="type">variant &amp;</span> <a href="variant.html#id1634032-bb"><span class="bold"><strong>operator</strong></span>=</a>(<span class="bold"><strong>const</strong></span> T &amp;);
54
55  <span class="emphasis"><em>// <a href="variant.html#id1572706-bb">queries</a></em></span>
56  <span class="type"><span class="bold"><strong>int</strong></span></span> <a href="variant.html#id1572710-bb">which</a>() <span class="bold"><strong>const</strong></span>;
57  <span class="type"><span class="bold"><strong>bool</strong></span></span> <a href="variant.html#id1631554-bb">empty</a>() <span class="bold"><strong>const</strong></span>;
58  <span class="type"><span class="bold"><strong>const</strong></span> std::type_info &amp;</span> <a href="variant.html#id1005344-bb">type</a>() <span class="bold"><strong>const</strong></span>;
59
60  <span class="emphasis"><em>// <a href="variant.html#id1636712-bb">relational</a></em></span>
61  <span class="type"><span class="bold"><strong>bool</strong></span></span> <a href="variant.html#id1011694-bb"><span class="bold"><strong>operator</strong></span>==</a>(<span class="bold"><strong>const</strong></span> variant &amp;) <span class="bold"><strong>const</strong></span>;
62  <span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> U&gt; <span class="type"><span class="bold"><strong>void</strong></span></span> <a href="variant.html#id1673222-bb"><span class="bold"><strong>operator</strong></span>==</a>(<span class="bold"><strong>const</strong></span> U &amp;) <span class="bold"><strong>const</strong></span>;
63  <span class="type"><span class="bold"><strong>bool</strong></span></span> <a href="variant.html#id1638199-bb"><span class="bold"><strong>operator</strong></span>&lt;</a>(<span class="bold"><strong>const</strong></span> variant &amp;) <span class="bold"><strong>const</strong></span>;
64  <span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> U&gt; <span class="type"><span class="bold"><strong>void</strong></span></span> <a href="variant.html#id1638215-bb"><span class="bold"><strong>operator</strong></span>&lt;</a>(<span class="bold"><strong>const</strong></span> U &amp;) <span class="bold"><strong>const</strong></span>;
65};</pre></div>
66<div class="refsect1" lang="en">
67<a name="id1944701"></a><h2>Description</h2>
68<p>The <code class="computeroutput">variant</code> class template (inspired by Andrei
69        Alexandrescu's class of the same name
70        [<a href="../variant/refs.html#variant.refs.ale01a">Ale01A</a>]) is an efficient,
71        <a href="../variant/tutorial.html#variant.tutorial.recursive" title="Recursive variant types">recursive-capable</a>,
72        bounded discriminated union value type capable of containing any value
73        type (either POD or non-POD). It supports construction from any type
74        convertible to one of its bounded types or from a source
75        <code class="computeroutput">variant</code> whose bounded types are each convertible to one
76        of the destination <code class="computeroutput">variant</code>'s bounded types. As well,
77        through <code class="computeroutput"><a href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code>,
78        <code class="computeroutput">variant</code> supports compile-time checked, type-safe
79        visitation; and through <code class="computeroutput"><a href="get.html" title="Function get">get</a></code>,
80        <code class="computeroutput">variant</code> supports run-time checked, type-safe value
81        retrieval.</p>
82<p><span class="bold"><strong>Notes</strong></span>:</p>
83<div class="itemizedlist"><ul type="disc">
84<li>The bounded types of the <code class="computeroutput">variant</code> are exposed
85            via the nested typedef <code class="computeroutput">types</code>, which is an
86            <a href="../../../libs/mpl/index.html" target="_top">MPL</a>-compatible Sequence containing the
87            set of types that must be handled by any
88            <a href="../variant/reference.html#variant.concepts.static-visitor" title="StaticVisitor">visitor</a> to
89            the <code class="computeroutput">variant</code>.</li>
90<li>All members of <code class="computeroutput">variant</code> satisfy at least the
91            basic guarantee of exception-safety. That is, all operations on
92            a <code class="computeroutput">variant</code> remain defined even after previous
93            operations have failed.</li>
94<li>Each type specified as a template argument to
95            <code class="computeroutput">variant</code> must meet the requirements of the
96            <span class="emphasis"><em><a href="../variant/reference.html#variant.concepts.bounded-type" title="BoundedType">BoundedType</a></em></span>
97            concept.</li>
98<li>Each type specified as a template argument to
99            <code class="computeroutput">variant</code> must be distinct after removal of qualifiers.
100            Thus, for instance, both <code class="computeroutput">variant&lt;int, int&gt;</code> and
101            <code class="computeroutput">variant&lt;int, const int&gt;</code> have undefined
102            behavior.</li>
103<li>Conforming implementations of <code class="computeroutput">variant</code> must
104            allow at least ten types as template arguments. The exact number
105            of allowed arguments is exposed by the preprocessor macro
106            <code class="computeroutput"><a href="../BOOST_VARIANT_LIMIT_TYPES.html" title="Macro BOOST_VARIANT_LIMIT_TYPES">BOOST_VARIANT_LIMIT_TYPES</a></code>.
107            (See <code class="computeroutput"><a href="make_variant_over.html" title="Class template make_variant_over">make_variant_over</a></code> for a
108            means to specify the bounded types of a <code class="computeroutput">variant</code> by
109            the elements of an <a href="../../../libs/mpl/index.html" target="_top">MPL</a> or compatible
110            Sequence, thus overcoming this limitation.)</li>
111</ul></div>
112<div class="refsect2" lang="en">
113<a name="id1944944"></a><h3>
114<a name="boost.variantconstruct-copy-destruct"></a><code class="computeroutput">variant</code> construct/copy/destruct</h3>
115<div class="orderedlist"><ol type="1">
116<li>
117<pre class="literallayout"><a name="id1602028-bb"></a>variant();</pre>
118<div class="variablelist"><table border="0">
119<col align="left" valign="top">
120<tbody>
121<tr>
122<td>
123<span class="term">Requires:</span></td>
124<td>The first bounded type of the <code class="computeroutput">variant</code> (i.e.,
125            <code class="computeroutput">T1</code>) must fulfill the requirements of the
126            <span class="emphasis"><em>DefaultConstructible</em></span> [20.1.4]
127            concept.</td>
128</tr>
129<tr>
130<td>
131<span class="term">Postconditions:</span></td>
132<td>Content of <code class="computeroutput">*this</code> is the default value of the
133            first bounded type (i.e, <code class="computeroutput">T1</code>).</td>
134</tr>
135<tr>
136<td>
137<span class="term">Throws:</span></td>
138<td>May fail with any exceptions arising from the default
139            constructor of <code class="computeroutput">T1</code>.</td>
140</tr>
141</tbody>
142</table></div>
143</li>
144<li>
145<pre class="literallayout"><a name="id1599613-bb"></a>variant(<span class="bold"><strong>const</strong></span> variant &amp; other);</pre>
146<div class="variablelist"><table border="0">
147<col align="left" valign="top">
148<tbody>
149<tr>
150<td>
151<span class="term">Postconditions:</span></td>
152<td>Content of <code class="computeroutput">*this</code> is a copy of the content of
153            <code class="computeroutput">other</code>.</td>
154</tr>
155<tr>
156<td>
157<span class="term">Throws:</span></td>
158<td>May fail with any exceptions arising from the
159            copy constructor of <code class="computeroutput">other</code>'s contained type.</td>
160</tr>
161</tbody>
162</table></div>
163</li>
164<li>
165<pre class="literallayout"><span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> T&gt; <a name="id1254269-bb"></a>variant(T &amp; operand);</pre>
166<div class="variablelist"><table border="0">
167<col align="left" valign="top">
168<tbody>
169<tr>
170<td>
171<span class="term">Requires:</span></td>
172<td>
173<code class="computeroutput">T</code> must be unambiguously convertible to one of
174            the bounded types (i.e., <code class="computeroutput">T1</code>, <code class="computeroutput">T2</code>,
175            etc.).</td>
176</tr>
177<tr>
178<td>
179<span class="term">Postconditions:</span></td>
180<td>Content of <code class="computeroutput">*this</code> is the best conversion of
181            <code class="computeroutput">operand</code> to one of the bounded types, as determined
182            by standard overload resolution rules.</td>
183</tr>
184<tr>
185<td>
186<span class="term">Throws:</span></td>
187<td>May fail with any exceptions arising from the conversion of
188            <code class="computeroutput">operand</code> to one of the bounded types.</td>
189</tr>
190</tbody>
191</table></div>
192</li>
193<li>
194<pre class="literallayout"><span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> T&gt; <a name="id1636459-bb"></a>variant(<span class="bold"><strong>const</strong></span> T &amp; operand);</pre>
195<div class="variablelist"><table border="0">
196<col align="left" valign="top">
197<tbody><tr>
198<td>
199<span class="term">Notes:</span></td>
200<td>Same semantics as previous constructor, but allows
201            construction from temporaries.</td>
202</tr></tbody>
203</table></div>
204</li>
205<li>
206<pre class="literallayout"><span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> U1, <span class="bold"><strong>typename</strong></span> U2, ..., <span class="bold"><strong>typename</strong></span> UN&gt; 
207  <a name="id1604404-bb"></a>variant(variant&lt;U1, U2, ..., UN&gt; &amp; operand);</pre>
208<div class="variablelist"><table border="0">
209<col align="left" valign="top">
210<tbody>
211<tr>
212<td>
213<span class="term">Requires:</span></td>
214<td>
215<span class="emphasis"><em>Every</em></span> one of <code class="computeroutput">U1</code>,
216            <code class="computeroutput">U2</code>, ..., <code class="computeroutput">UN</code> must have an unambiguous
217            conversion to one of the bounded types (i.e., <code class="computeroutput">T1</code>,
218            <code class="computeroutput">T2</code>, ..., <code class="computeroutput">TN</code>).</td>
219</tr>
220<tr>
221<td>
222<span class="term">Postconditions:</span></td>
223<td>If <code class="computeroutput">variant&lt;U1, U2, ..., UN&gt;</code> is itself
224            one of the bounded types, then content of <code class="computeroutput">*this</code> is a
225            copy of <code class="computeroutput">operand</code>. Otherwise, content of
226            <code class="computeroutput">*this</code> is the best conversion of the content of
227            <code class="computeroutput">operand</code> to one of the bounded types, as determined
228            by standard overload resolution rules.</td>
229</tr>
230<tr>
231<td>
232<span class="term">Throws:</span></td>
233<td>If <code class="computeroutput">variant&lt;U1, U2, ..., UN&gt;</code> is itself
234          one of the bounded types, then may fail with any exceptions arising
235          from the copy constructor of
236          <code class="computeroutput">variant&lt;U1, U2, ..., UN&gt;</code>. Otherwise, may fail
237          with any exceptions arising from the conversion of the content of
238          <code class="computeroutput">operand</code> to one of the bounded types.</td>
239</tr>
240</tbody>
241</table></div>
242</li>
243<li>
244<pre class="literallayout"><span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> U1, <span class="bold"><strong>typename</strong></span> U2, ..., <span class="bold"><strong>typename</strong></span> UN&gt; 
245  <a name="id1630438-bb"></a>variant(<span class="bold"><strong>const</strong></span> variant&lt;U1, U2, ..., UN&gt; &amp; operand);</pre>
246<div class="variablelist"><table border="0">
247<col align="left" valign="top">
248<tbody><tr>
249<td>
250<span class="term">Notes:</span></td>
251<td>Same semantics as previous constructor, but allows
252            construction from temporaries.</td>
253</tr></tbody>
254</table></div>
255</li>
256<li>
257<pre class="literallayout"><a name="id1601741-bb"></a>~variant();</pre>
258<div class="variablelist"><table border="0">
259<col align="left" valign="top">
260<tbody>
261<tr>
262<td>
263<span class="term">Effects:</span></td>
264<td>Destroys the content of <code class="computeroutput">*this</code>.</td>
265</tr>
266<tr>
267<td>
268<span class="term">Throws:</span></td>
269<td>Will not throw.</td>
270</tr>
271</tbody>
272</table></div>
273</li>
274</ol></div>
275</div>
276<div class="refsect2" lang="en">
277<a name="id1945483"></a><h3>
278<a name="id790460-bb"></a><code class="computeroutput">variant</code> modifiers</h3>
279<div class="orderedlist"><ol type="1">
280<li>
281<pre class="literallayout"><span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id790464-bb"></a>swap(variant &amp; other);</pre>
282<div class="variablelist"><table border="0">
283<col align="left" valign="top">
284<tbody>
285<tr>
286<td>
287<span class="term">Requires:</span></td>
288<td>Every bounded type must fulfill the requirements of the
289              <a href="../Assignable.html" title="Concept Assignable">Assignable</a>
290              concept.</td>
291</tr>
292<tr>
293<td>
294<span class="term">Effects:</span></td>
295<td>Interchanges the content of <code class="computeroutput">*this</code> and
296              <code class="computeroutput">other</code>.</td>
297</tr>
298<tr>
299<td>
300<span class="term">Throws:</span></td>
301<td>If the contained type of <code class="computeroutput">other</code> is the same as
302              the contained type of <code class="computeroutput">*this</code>, then may fail with any
303              exceptions arising from the <code class="computeroutput">swap</code> of the contents of
304              <code class="computeroutput">*this</code> and <code class="computeroutput">other</code>. Otherwise, may fail
305              with any exceptions arising from either of the copy constructors
306              of the contained types. Also, in the event of insufficient
307              memory, may fail with <code class="computeroutput">std::bad_alloc</code>
308              (<a href="../variant/design.html#variant.design.never-empty.problem" title="The Implementation Problem">why?</a>).</td>
309</tr>
310</tbody>
311</table></div>
312</li>
313<li>
314<pre class="literallayout"><span class="type">variant &amp;</span> <a name="id1669309-bb"></a><span class="bold"><strong>operator</strong></span>=(<span class="bold"><strong>const</strong></span> variant &amp; rhs);</pre>
315<div class="variablelist"><table border="0">
316<col align="left" valign="top">
317<tbody>
318<tr>
319<td>
320<span class="term">Requires:</span></td>
321<td>Every bounded type must fulfill the requirements of the
322              <a href="../Assignable.html" title="Concept Assignable">Assignable</a>
323              concept.</td>
324</tr>
325<tr>
326<td>
327<span class="term">Effects:</span></td>
328<td>If the contained type of <code class="computeroutput">rhs</code> is the same as
329              the contained type of <code class="computeroutput">*this</code>, then assigns the
330              content of <code class="computeroutput">rhs</code> into the content of
331              <code class="computeroutput">*this</code>. Otherwise, makes the content of
332              <code class="computeroutput">*this</code> a copy of the content of <code class="computeroutput">rhs</code>,
333              destroying the previous content of <code class="computeroutput">*this</code>.</td>
334</tr>
335<tr>
336<td>
337<span class="term">Throws:</span></td>
338<td>If the contained type of <code class="computeroutput">rhs</code> is the same as
339              the contained type of <code class="computeroutput">*this</code>, then may fail with any
340              exceptions arising from the assignment of the content of
341              <code class="computeroutput">rhs</code> into the content <code class="computeroutput">*this</code>. Otherwise,
342              may fail with any exceptions arising from the copy constructor
343              of the contained type of <code class="computeroutput">rhs</code>. Also, in the event of
344              insufficient memory, may fail with <code class="computeroutput">std::bad_alloc</code>
345              (<a href="../variant/design.html#variant.design.never-empty.problem" title="The Implementation Problem">why?</a>).</td>
346</tr>
347</tbody>
348</table></div>
349</li>
350<li>
351<pre class="literallayout"><span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> T&gt; <span class="type">variant &amp;</span> <a name="id1634032-bb"></a><span class="bold"><strong>operator</strong></span>=(<span class="bold"><strong>const</strong></span> T &amp; rhs);</pre>
352<div class="variablelist"><table border="0">
353<col align="left" valign="top">
354<tbody>
355<tr>
356<td>
357<span class="term">Requires:</span></td>
358<td><div class="itemizedlist"><ul type="disc">
359<li>
360<code class="computeroutput">T</code> must be unambiguously convertible to
361                one of the bounded types (i.e., <code class="computeroutput">T1</code>,
362                <code class="computeroutput">T2</code>, etc.).</li>
363<li>Every bounded type must fulfill the requirements of the
364                <a href="../Assignable.html" title="Concept Assignable">Assignable</a>
365                concept.</li>
366</ul></div></td>
367</tr>
368<tr>
369<td>
370<span class="term">Effects:</span></td>
371<td>If the contained type of <code class="computeroutput">*this</code> is
372              <code class="computeroutput">T</code>, then assigns <code class="computeroutput">rhs</code> into the content
373              of <code class="computeroutput">*this</code>. Otherwise, makes the content of
374              <code class="computeroutput">*this</code> the best conversion of <code class="computeroutput">rhs</code> to
375              one of the bounded types, as determined by standard overload
376              resolution rules, destroying the previous content of
377              <code class="computeroutput">*this</code>.</td>
378</tr>
379<tr>
380<td>
381<span class="term">Throws:</span></td>
382<td>If the contained type of <code class="computeroutput">*this</code> is
383              <code class="computeroutput">T</code>, then may fail with any exceptions arising from
384              the assignment of <code class="computeroutput">rhs</code> into the content
385              <code class="computeroutput">*this</code>. Otherwise, may fail with any exceptions
386              arising from the conversion of <code class="computeroutput">rhs</code> to one of the
387              bounded types. Also, in the event of insufficient memory, may
388              fail with <code class="computeroutput">std::bad_alloc</code>
389              (<a href="../variant/design.html#variant.design.never-empty.problem" title="The Implementation Problem">why?</a>).</td>
390</tr>
391</tbody>
392</table></div>
393</li>
394</ol></div>
395</div>
396<div class="refsect2" lang="en">
397<a name="id1945960"></a><h3>
398<a name="id1572706-bb"></a><code class="computeroutput">variant</code> queries</h3>
399<div class="orderedlist"><ol type="1">
400<li>
401<pre class="literallayout"><span class="type"><span class="bold"><strong>int</strong></span></span> <a name="id1572710-bb"></a>which() <span class="bold"><strong>const</strong></span>;</pre>
402<div class="variablelist"><table border="0">
403<col align="left" valign="top">
404<tbody>
405<tr>
406<td>
407<span class="term">Returns:</span></td>
408<td>The zero-based index into the set of bounded types
409              of the contained type of <code class="computeroutput">*this</code>. (For instance, if
410              called on a <code class="computeroutput">variant&lt;int, std::string&gt;</code> object
411              containing a <code class="computeroutput">std::string</code>, <code class="computeroutput">which()</code>
412              would return <code class="computeroutput">1</code>.)</td>
413</tr>
414<tr>
415<td>
416<span class="term">Throws:</span></td>
417<td>Will not throw.</td>
418</tr>
419</tbody>
420</table></div>
421</li>
422<li>
423<pre class="literallayout"><span class="type"><span class="bold"><strong>bool</strong></span></span> <a name="id1631554-bb"></a>empty() <span class="bold"><strong>const</strong></span>;</pre>
424<div class="variablelist"><table border="0">
425<col align="left" valign="top">
426<tbody>
427<tr>
428<td>
429<span class="term">Returns:</span></td>
430<td>
431<code class="computeroutput">false</code>: <code class="computeroutput">variant</code> always contains
432              exactly one of its bounded types. (See
433              <a href="../variant/design.html#variant.design.never-empty" title='"Never-Empty" Guarantee'>the section called &#8220;"Never-Empty" Guarantee&#8221;</a>
434              for more information.)</td>
435</tr>
436<tr>
437<td>
438<span class="term">Rationale:</span></td>
439<td>Facilitates generic compatibility with
440              <a href="any.html" title="Class any">boost::any</a>.</td>
441</tr>
442<tr>
443<td>
444<span class="term">Throws:</span></td>
445<td>Will not throw.</td>
446</tr>
447</tbody>
448</table></div>
449</li>
450<li>
451<pre class="literallayout"><span class="type"><span class="bold"><strong>const</strong></span> std::type_info &amp;</span> <a name="id1005344-bb"></a>type() <span class="bold"><strong>const</strong></span>;</pre>
452<div class="variablelist"><table border="0">
453<col align="left" valign="top">
454<tbody>
455<tr>
456<td>
457<span class="term">Returns:</span></td>
458<td>
459<code class="computeroutput">typeid(x)</code>, where <code class="computeroutput">x</code> is the the
460              content of <code class="computeroutput">*this</code>.</td>
461</tr>
462<tr>
463<td>
464<span class="term">Throws:</span></td>
465<td>Will not throw.</td>
466</tr>
467</tbody>
468</table></div>
469</li>
470</ol></div>
471</div>
472<div class="refsect2" lang="en">
473<a name="id1946192"></a><h3>
474<a name="id1636712-bb"></a><code class="computeroutput">variant</code> relational</h3>
475<div class="orderedlist"><ol type="1">
476<li>
477<p><a name="id1636716-bb"></a></p>
478<pre class="literallayout"><span class="type"><span class="bold"><strong>bool</strong></span></span> <a name="id1011694-bb"></a><span class="bold"><strong>operator</strong></span>==(<span class="bold"><strong>const</strong></span> variant &amp; rhs) <span class="bold"><strong>const</strong></span>;
479<span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> U&gt; <span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id1673222-bb"></a><span class="bold"><strong>operator</strong></span>==(<span class="bold"><strong>const</strong></span> U &amp;) <span class="bold"><strong>const</strong></span>;</pre>
480<div class="variablelist"><table border="0">
481<col align="left" valign="top">
482<tbody>
483<tr>
484<td>
485<span class="term">Notes:</span></td>
486<td>The overload returning <code class="computeroutput">void</code> exists only to
487              prohibit implicit conversion of the operator's right-hand side
488              to <code class="computeroutput">variant</code>; thus, its use will (purposefully)
489              result in a compile-time error.</td>
490</tr>
491<tr>
492<td>
493<span class="term">Requires:</span></td>
494<td>Every bounded type of the <code class="computeroutput">variant</code> must
495              fulfill the requirements of the
496              <a href="../EqualityComparable.html" title="Concept EqualityComparable">EqualityComparable</a>
497              concept.</td>
498</tr>
499<tr>
500<td>
501<span class="term">Returns:</span></td>
502<td>
503<code class="computeroutput">true</code> iff <code class="computeroutput">which() == rhs.which()</code>
504              <span class="emphasis"><em>and</em></span>
505              <code class="computeroutput">content_this == content_rhs</code>, where
506              <code class="computeroutput">content_this</code> is the content of <code class="computeroutput">*this</code>
507              and <code class="computeroutput">content_rhs</code> is the content of
508              <code class="computeroutput">rhs</code>.</td>
509</tr>
510<tr>
511<td>
512<span class="term">Throws:</span></td>
513<td>If <code class="computeroutput">which() == rhs.which()</code> then may fail with
514              any exceptions arising from <code class="computeroutput">operator==(T,T)</code>, where
515              <code class="computeroutput">T</code> is the contained type of
516              <code class="computeroutput">*this</code>.</td>
517</tr>
518</tbody>
519</table></div>
520</li>
521<li>
522<p><a name="id1638192-bb"></a></p>
523<pre class="literallayout"><span class="type"><span class="bold"><strong>bool</strong></span></span> <a name="id1638199-bb"></a><span class="bold"><strong>operator</strong></span>&lt;(<span class="bold"><strong>const</strong></span> variant &amp; rhs) <span class="bold"><strong>const</strong></span>;
524<span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> U&gt; <span class="type"><span class="bold"><strong>void</strong></span></span> <a name="id1638215-bb"></a><span class="bold"><strong>operator</strong></span>&lt;(<span class="bold"><strong>const</strong></span> U &amp;) <span class="bold"><strong>const</strong></span>;</pre>
525<div class="variablelist"><table border="0">
526<col align="left" valign="top">
527<tbody>
528<tr>
529<td>
530<span class="term">Notes:</span></td>
531<td>The overload returning <code class="computeroutput">void</code> exists only to
532              prohibit implicit conversion of the operator's right-hand side
533              to <code class="computeroutput">variant</code>; thus, its use will (purposefully)
534              result in a compile-time error.</td>
535</tr>
536<tr>
537<td>
538<span class="term">Requires:</span></td>
539<td>Every bounded type of the <code class="computeroutput">variant</code> must
540              fulfill the requirements of the
541              <a href="../LessThanComparable.html" title="Concept LessThanComparable">LessThanComparable</a>
542              concept.</td>
543</tr>
544<tr>
545<td>
546<span class="term">Returns:</span></td>
547<td>If <code class="computeroutput">which() == rhs.which()</code> then:
548              <code class="computeroutput">content_this &lt; content_rhs</code>, where
549              <code class="computeroutput">content_this</code> is the content of <code class="computeroutput">*this</code>
550              and <code class="computeroutput">content_rhs</code> is the content of <code class="computeroutput">rhs</code>.
551              Otherwise: <code class="computeroutput">which() &lt; rhs.which()</code>.</td>
552</tr>
553<tr>
554<td>
555<span class="term">Throws:</span></td>
556<td>If <code class="computeroutput">which() == rhs.which()</code> then may fail with
557              any exceptions arising from <code class="computeroutput">operator&lt;(T,T)</code>,
558              where <code class="computeroutput">T</code> is the contained type of
559              <code class="computeroutput">*this</code>.</td>
560</tr>
561</tbody>
562</table></div>
563</li>
564</ol></div>
565</div>
566</div>
567</div>
568<table width="100%"><tr>
569<td align="left"></td>
570<td align="right"><small>Copyright © 2002, 2003 Eric Friedman, Itay Maman</small></td>
571</tr></table>
572<hr>
573<div class="spirit-nav">
574<a accesskey="p" href="../BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../variant/reference.html#header.boost.variant.variant.hpp"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="../id1599586-bb.html"><img src="../images/next.png" alt="Next"></a>
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