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28<h2><span class="refentrytitle">Function apply_visitor</span></h2>
29<p>boost::apply_visitor &#8212; <p>Allows compile-time checked type-safe application of the
30        given visitor to the content of the given variant, ensuring that all
31        types are handled by the visitor.</p></p>
32</div>
33<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
34<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis">
35<span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> Visitor, <span class="bold"><strong>typename</strong></span> Variant&gt; 
36  <span class="type"><span class="bold"><strong>typename</strong></span> Visitor::result_type</span> 
37  apply_visitor(Visitor &amp; visitor, Variant &amp; operand);
38<span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> Visitor, <span class="bold"><strong>typename</strong></span> Variant&gt; 
39  <span class="type"><span class="bold"><strong>typename</strong></span> Visitor::result_type</span> 
40  apply_visitor(<span class="bold"><strong>const</strong></span> Visitor &amp; visitor, Variant &amp; operand);
41<span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> BinaryVisitor, <span class="bold"><strong>typename</strong></span> Variant1, <span class="bold"><strong>typename</strong></span> Variant2&gt; 
42  <span class="type"><span class="bold"><strong>typename</strong></span> BinaryVisitor::result_type</span> 
43  apply_visitor(BinaryVisitor &amp; visitor, Variant1 &amp; operand1,
44                Variant2 &amp; operand2);
45<span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> BinaryVisitor, <span class="bold"><strong>typename</strong></span> Variant1, <span class="bold"><strong>typename</strong></span> Variant2&gt; 
46  <span class="type"><span class="bold"><strong>typename</strong></span> BinaryVisitor::result_type</span> 
47  apply_visitor(<span class="bold"><strong>const</strong></span> BinaryVisitor &amp; visitor, Variant1 &amp; operand1,
48                Variant2 &amp; operand2);
49<span class="bold"><strong>template</strong></span>&lt;<span class="bold"><strong>typename</strong></span> Visitor&gt; 
50  <span class="type"><a href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">apply_visitor_delayed_t</a>&lt;Visitor&gt;</span> apply_visitor(Visitor &amp; visitor);</pre></div>
51<div class="refsect1" lang="en">
52<a name="id2838602"></a><h2>Description</h2>
53<p>The behavior of <code class="computeroutput">apply_visitor</code> is dependent on
54        the number of arguments on which it operates (i.e., other than the
55        visitor). The function behaves as follows:
56
57          <div class="itemizedlist"><ul type="disc">
58<li>Overloads accepting one operand invoke the unary function
59              call operator of the given visitor on the content of the given
60              <code class="computeroutput"><a href="boost/variant.html" title="Class template variant">variant</a></code> operand.</li>
61<li>Overloads accepting two operands invoke the binary
62              function call operator of the given visitor on the content of
63              the given <code class="computeroutput"><a href="boost/variant.html" title="Class template variant">variant</a></code>
64              operands.</li>
65<li>The overload accepting only a visitor returns a
66              <code class="computeroutput"><a href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">generic function object</a></code>
67              that accepts either one or two arguments and invokes
68              <code class="computeroutput"><a href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code> using
69              these arguments and <code class="computeroutput">visitor</code>, thus behaving as
70              specified above. (This behavior is particularly useful, for
71              example, when one needs to operate on each element of a sequence
72              of variant objects using a standard library
73              algorithm.)</li>
74</ul></div></p>
75<p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Returns</span></b>:
76
77    The overloads acccepting operands return the result of
78        applying the given visitor to the content of the given operands.
79        The overload accepting only a visitor return a function object, thus
80        delaying application of the visitor to any operands.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Requires</span></b>:
81
82    The given visitor must fulfill the
83        <a href="variant/reference.html#variant.concepts.static-visitor" title="StaticVisitor"><span class="emphasis"><em>StaticVisitor</em></span></a>
84        concept requirements with respect to each of the bounded types of the
85        given <code class="computeroutput">variant</code>.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Throws</span></b>:
86
87    The overloads accepting operands throw only if the given
88        visitor throws when applied. The overload accepting only a visitor
89        will not throw. (Note, however, that the returned
90        <a href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">function object</a>
91        may throw when invoked.)</p>
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