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<title>Function apply_visitor</title>
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<div class="refentry">
<a name="boost.apply_visitor"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Function apply_visitor</span></h2>
<p>boost::apply_visitor — Allows compile-time checked type-safe application of the
given visitor to the content of the given variant, ensuring that all
types are handled by the visitor.</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.apply_visitor_hpp" title="Header <boost/variant/apply_visitor.hpp>">boost/variant/apply_visitor.hpp</a>>
</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Visitor<span class="special">,</span> <span class="keyword">typename</span> Variant<span class="special">></span>
<span class="keyword">typename</span> <span class="identifier">Visitor</span><span class="special">::</span><span class="identifier">result_type</span>
<span class="identifier">apply_visitor</span><span class="special">(</span><span class="identifier">Visitor</span> <span class="special">&</span> visitor<span class="special">,</span> <span class="identifier">Variant</span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Visitor<span class="special">,</span> <span class="keyword">typename</span> Variant<span class="special">></span>
<span class="keyword">typename</span> <span class="identifier">Visitor</span><span class="special">::</span><span class="identifier">result_type</span>
<span class="identifier">apply_visitor</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Visitor</span> <span class="special">&</span> visitor<span class="special">,</span> <span class="identifier">Variant</span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> BinaryVisitor<span class="special">,</span> <span class="keyword">typename</span> Variant1<span class="special">,</span> <span class="keyword">typename</span> Variant2<span class="special">></span>
<span class="keyword">typename</span> <span class="identifier">BinaryVisitor</span><span class="special">::</span><span class="identifier">result_type</span>
<span class="identifier">apply_visitor</span><span class="special">(</span><span class="identifier">BinaryVisitor</span> <span class="special">&</span> visitor<span class="special">,</span> <span class="identifier">Variant1</span> <span class="special">&</span> operand1<span class="special">,</span>
<span class="identifier">Variant2</span> <span class="special">&</span> operand2<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> BinaryVisitor<span class="special">,</span> <span class="keyword">typename</span> Variant1<span class="special">,</span> <span class="keyword">typename</span> Variant2<span class="special">></span>
<span class="keyword">typename</span> <span class="identifier">BinaryVisitor</span><span class="special">::</span><span class="identifier">result_type</span>
<span class="identifier">apply_visitor</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">BinaryVisitor</span> <span class="special">&</span> visitor<span class="special">,</span> <span class="identifier">Variant1</span> <span class="special">&</span> operand1<span class="special">,</span>
<span class="identifier">Variant2</span> <span class="special">&</span> operand2<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> MultiVisitor<span class="special">,</span> <span class="keyword">typename</span> Variant1<span class="special">,</span> <span class="keyword">typename</span> Variant2<span class="special">,</span>
<span class="keyword">typename</span> Variant3<span class="special">></span>
<span class="keyword">typename</span> <span class="identifier">MultiVisitor</span><span class="special">::</span><span class="identifier">result_type</span>
<span class="identifier">apply_visitor</span><span class="special">(</span><span class="identifier">MultiVisitor</span> <span class="special">&</span> visitor<span class="special">,</span> <span class="identifier">Variant1</span> <span class="special">&</span> operand1<span class="special">,</span>
<span class="identifier">Variant2</span> <span class="special">&</span> operand2<span class="special">,</span> <span class="identifier">Variant3</span> <span class="special">&</span> operand3<span class="special">,</span> <span class="special">...</span> other_operands<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> MultiVisitor<span class="special">,</span> <span class="keyword">typename</span> Variant1<span class="special">,</span> <span class="keyword">typename</span> Variant2<span class="special">,</span>
<span class="keyword">typename</span> Variant3<span class="special">></span>
<span class="keyword">typename</span> <span class="identifier">MultiVisitor</span><span class="special">::</span><span class="identifier">result_type</span>
<span class="identifier">apply_visitor</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">MultiVisitor</span> <span class="special">&</span> visitor<span class="special">,</span> <span class="identifier">Variant1</span> <span class="special">&</span> operand1<span class="special">,</span>
<span class="identifier">Variant2</span> <span class="special">&</span> operand2<span class="special">,</span> <span class="identifier">Variant3</span> <span class="special">&</span> operand3<span class="special">,</span> <span class="special">...</span> other_operands<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Visitor<span class="special">></span>
<a class="link" href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">apply_visitor_delayed_t</a><span class="special"><</span><span class="identifier">Visitor</span><span class="special">></span> <span class="identifier">apply_visitor</span><span class="special">(</span><span class="identifier">Visitor</span> <span class="special">&</span> visitor<span class="special">)</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp250407688"></a><h2>Description</h2>
<p>The behavior of <code class="computeroutput">apply_visitor</code> is dependent on
the number of arguments on which it operates (i.e., other than the
visitor). The function behaves as follows:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">Overloads accepting one operand invoke the unary function
call operator of the given visitor on the content of the given
<code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code> operand.</li>
<li class="listitem">Overloads accepting two operands invoke the binary
function call operator of the given visitor on the content of
the given <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code>
operands.</li>
<li class="listitem">Overloads accepting three or more operands invoke the
function call operator of the given visitor on the content of
the given <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code>
operands. Maximum amount of parameters controlled by
<code class="computeroutput"><span class="bold"><strong><a class="link" href="../BOOST_VARAINT_MAX_MULTIVIZITOR_PARAMS.html" title="Macro BOOST_VARAINT_MAX_MULTIVIZITOR_PARAMS">BOOST_VARAINT_MAX_MULTIVIZITOR_PARAMS</a></strong></span></code>
macro. Those functions are actually defined in <a class="xref" href="../variant/reference.html#header.boost.variant.multivisitors_hpp" title="Header <boost/variant/multivisitors.hpp>">the section called “Header <boost/variant/multivisitors.hpp>”</a>.</li>
<li class="listitem">The overload accepting only a visitor returns a
<code class="computeroutput"><a class="link" href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">generic function object</a></code>
that accepts either one or two arguments and invokes
<code class="computeroutput"><a class="link" href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code> using
these arguments and <code class="computeroutput">visitor</code>, thus behaving as
specified above. (This behavior is particularly useful, for
example, when one needs to operate on each element of a sequence
of variant objects using a standard library
algorithm.)</li>
</ul></div>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td>The overloads acccepting operands return the result of
applying the given visitor to the content of the given operands.
The overload accepting only a visitor return a function object, thus
delaying application of the visitor to any operands.</td>
</tr>
<tr>
<td><p><span class="term">Requires:</span></p></td>
<td>The given visitor must fulfill the
<a class="link" href="../variant/reference.html#variant.concepts.static-visitor" title="StaticVisitor"><span class="emphasis"><em>StaticVisitor</em></span></a>
concept requirements with respect to each of the bounded types of the
given <code class="computeroutput">variant</code>.</td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td>The overloads accepting operands throw only if the given
visitor throws when applied. The overload accepting only a visitor
will not throw. (Note, however, that the returned
<a class="link" href="apply_visitor_delayed_t.html" title="Class template apply_visitor_delayed_t">function object</a>
may throw when invoked.)</td>
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<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>)
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