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   5 <title>Function relaxed_get</title>
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  26 <div class="refentry">
  27 <a name="boost.relaxed_get"></a><div class="titlepage"></div>
  28 <div class="refnamediv">
  29 <h2><span class="refentrytitle">Function relaxed_get</span></h2>
  30 <p>boost::relaxed_get &#8212; Retrieves a value of a specified type from a given
  31           <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code>. Unlike <a class="link" href="strict_get.html" title="Function strict_get">strict_get</a> does not assert at compile time
  32         that type <code class="computeroutput">U</code> is one of the types that can be stored in variant.</p>
  33 </div>
  34 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  35 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../variant/reference.html#header.boost.variant.get_hpp" title="Header &lt;boost/variant/get.hpp&gt;">boost/variant/get.hpp</a>&gt;
  36
  37 </span>
  38 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<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="special">...</span><span class="special">,</span> <span class="keyword">typename</span> TN<span class="special">&gt;</span>
  39   <span class="identifier">U</span> <span class="special">*</span> <span class="identifier">relaxed_get</span><span class="special">(</span><a class="link" href="variant.html" title="Class template variant">variant</a><span class="special">&lt;</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">&gt;</span> <span class="special">*</span> operand<span class="special">)</span><span class="special">;</span>
  40 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<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="special">...</span><span class="special">,</span> <span class="keyword">typename</span> TN<span class="special">&gt;</span>
  41   <span class="keyword">const</span> <span class="identifier">U</span> <span class="special">*</span> <span class="identifier">relaxed_get</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="variant.html" title="Class template variant">variant</a><span class="special">&lt;</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">&gt;</span> <span class="special">*</span> operand<span class="special">)</span><span class="special">;</span>
  42 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<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="special">...</span><span class="special">,</span> <span class="keyword">typename</span> TN<span class="special">&gt;</span>
  43   <span class="identifier">U</span> <span class="special">&amp;</span> <span class="identifier">relaxed_get</span><span class="special">(</span><a class="link" href="variant.html" title="Class template variant">variant</a><span class="special">&lt;</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">&gt;</span> <span class="special">&amp;</span> operand<span class="special">)</span><span class="special">;</span>
  44 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<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="special">...</span><span class="special">,</span> <span class="keyword">typename</span> TN<span class="special">&gt;</span>
  45   <span class="keyword">const</span> <span class="identifier">U</span> <span class="special">&amp;</span> <span class="identifier">relaxed_get</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="variant.html" title="Class template variant">variant</a><span class="special">&lt;</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">&gt;</span> <span class="special">&amp;</span> operand<span class="special">)</span><span class="special">;</span></pre></div>
  46 <div class="refsect1">
  47 <a name="idp616146912"></a><h2>Description</h2>
  48 <p>The <code class="computeroutput">get</code> function allows run-time checked,
  49           type-safe retrieval of the content of the given
  50           <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code>. The function succeeds
  51           only if the content is of the specified type <code class="computeroutput">U</code>, with
  52           failure indicated as described below.</p>
  53 <p><span class="bold"><strong>Recomendation</strong></span>: Use
  54           <code class="computeroutput"><a class="link" href="get_idp777944992.html" title="Function get">get</a></code> or <code class="computeroutput"><a class="link" href="strict_get.html" title="Function strict_get">strict_get</a></code> in new code.
  55           <code class="computeroutput"><a class="link" href="strict_get.html" title="Function strict_get">strict_get</a></code>
  56           provides more compile time checks and its behavior is closer to <code class="computeroutput">std::get</code>
  57           from C++ Standard Library.</p>
  58 <p><span class="bold"><strong>Warning</strong></span>: After either
  59           <code class="computeroutput">operand</code> or its content is destroyed (e.g., when the
  60           given <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code> is assigned a
  61           value of different type), the returned reference is invalidated.
  62           Thus, significant care and caution must be extended when handling
  63           the returned reference.</p>
  64 <div class="variablelist"><table border="0" class="variablelist compact">
  65 <colgroup>
  66 <col align="left" valign="top">
  67 <col>
  68 </colgroup>
  69 <tbody>
  70 <tr>
  71 <td><p><span class="term">Notes:</span></p></td>
  72 <td>As part of its guarantee of type-safety, <code class="computeroutput">get</code>
  73         enforces <code class="computeroutput">const</code>-correctness. Thus, the specified type
  74         <code class="computeroutput">U</code> must be <code class="computeroutput">const</code>-qualified whenever
  75         <code class="computeroutput">operand</code> or its content is likewise
  76         <code class="computeroutput">const</code>-qualified. The converse, however, is not required:
  77         that is, the specified type <code class="computeroutput">U</code> may be
  78         <code class="computeroutput">const</code>-qualified even when <code class="computeroutput">operand</code> and its
  79         content are not.</td>
  80 </tr>
  81 <tr>
  82 <td><p><span class="term">Returns:</span></p></td>
  83 <td>If passed a pointer, <code class="computeroutput">get</code> returns a pointer to
  84         the value content if it is of the specified type <code class="computeroutput">U</code>;
  85         otherwise, a null pointer is returned. If passed a reference,
  86         <code class="computeroutput">get</code> returns a reference to the value content if it is of
  87         the specified type <code class="computeroutput">U</code>; otherwise, an exception is thrown
  88         (see below).</td>
  89 </tr>
  90 <tr>
  91 <td><p><span class="term">Throws:</span></p></td>
  92 <td>Overloads taking a
  93         <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code> pointer will not
  94         throw; the overloads taking a
  95         <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code> reference throw
  96         <code class="computeroutput"><a class="link" href="bad_get.html" title="Class bad_get">bad_get</a></code> if the content is not of
  97         the specified type <code class="computeroutput">U</code>.</td>
  98 </tr>
  99 <tr>
 100 <td><p><span class="term">Rationale:</span></p></td>
 101 <td>While visitation via
 102         <code class="computeroutput"><a class="link" href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code>
 103         is generally preferred due to its greater safety, <code class="computeroutput">get</code> may
 104         may be more convenient in some cases due to its straightforward
 105         usage.</td>
 106 </tr>
 107 </tbody>
 108 </table></div>
 109 </div>
 110 </div>
 111 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 112 <td align="left"></td>
 113 <td align="right"><div class="copyright-footer">Copyright &#169; 2002, 2003 Eric Friedman, Itay Maman<p>Distributed under the Boost Software License, Version 1.0.
 114     (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at
 115     <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 116     </p>
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