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  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="core.explicit_operator_bool"></a><a class="link" href="explicit_operator_bool.html" title="explicit_operator_bool">explicit_operator_bool</a>
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  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="explicit_operator_bool.html#core.explicit_operator_bool.overview">Overview</a></span></dt>
  31 <dt><span class="section"><a href="explicit_operator_bool.html#core.explicit_operator_bool.examples">Examples</a></span></dt>
  32 <dt><span class="section"><a href="explicit_operator_bool.html#core.explicit_operator_bool.history">History</a></span></dt>
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  35 <div class="titlepage"><div><div><h3 class="title">
  36 <a name="idm46687075747984"></a>Authors</h3></div></div></div>
  37 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
  38           Andrey Semashev
  39         </li></ul></div>
  40 </div>
  41 <div class="section">
  42 <div class="titlepage"><div><div><h3 class="title">
  43 <a name="core.explicit_operator_bool.overview"></a><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.overview" title="Overview">Overview</a>
  44 </h3></div></div></div>
  45 <p>
  46         Header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">core</span><span class="special">/</span><span class="identifier">explicit_operator_bool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  47         provides <code class="computeroutput"><span class="identifier">BOOST_EXPLICIT_OPERATOR_BOOL</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL</span><span class="special">()</span></code> compatibility helper macros that expand
  48         to an explicit conversion operator to <code class="computeroutput"><span class="keyword">bool</span></code>.
  49         For compilers not supporting explicit conversion operators introduced in
  50         C++11 the macros expand to a conversion operator that implements the <a href="http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Safe_bool" target="_top">safe bool
  51         idiom</a>. In case if the compiler is not able to handle safe bool idiom
  52         well the macros expand to a regular conversion operator to <code class="computeroutput"><span class="keyword">bool</span></code>.
  53       </p>
  54 </div>
  55 <div class="section">
  56 <div class="titlepage"><div><div><h3 class="title">
  57 <a name="core.explicit_operator_bool.examples"></a><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.examples" title="Examples">Examples</a>
  58 </h3></div></div></div>
  59 <p>
  60         Both macros are intended to be placed within a user's class definition. The
  61         generated conversion operators will be implemented in terms of <code class="computeroutput"><span class="keyword">operator</span><span class="special">!()</span></code>
  62         that should be defined by user in this class. In case of <code class="computeroutput"><span class="identifier">BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL</span><span class="special">()</span></code> the generated conversion operator will
  63         be declared <code class="computeroutput"><span class="keyword">constexpr</span></code> which
  64         requires the corresponding <code class="computeroutput"><span class="keyword">operator</span><span class="special">!()</span></code> to also be <code class="computeroutput"><span class="keyword">constexpr</span></code>.
  65       </p>
  66 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">T</span> <span class="special">&gt;</span>
  67 <span class="keyword">class</span> <span class="identifier">my_ptr</span>
  68 <span class="special">{</span>
  69     <span class="identifier">T</span><span class="special">*</span> <span class="identifier">m_p</span><span class="special">;</span>
  70
  71 <span class="keyword">public</span><span class="special">:</span>
  72     <span class="identifier">BOOST_EXPLICIT_OPERATOR_BOOL</span><span class="special">()</span>
  73
  74     <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span>
  75     <span class="special">{</span>
  76         <span class="keyword">return</span> <span class="special">!</span><span class="identifier">m_p</span><span class="special">;</span>
  77     <span class="special">}</span>
  78 <span class="special">};</span>
  79 </pre>
  80 <p>
  81         Now <code class="computeroutput"><span class="identifier">my_ptr</span></code> can be used in
  82         conditional expressions, similarly to a regular pointer:
  83       </p>
  84 <pre class="programlisting"><span class="identifier">my_ptr</span><span class="special">&lt;</span> <span class="keyword">int</span> <span class="special">&gt;</span> <span class="identifier">p</span><span class="special">;</span>
  85 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">p</span><span class="special">)</span>
  86     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"true"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
  87 </pre>
  88 </div>
  89 <div class="section">
  90 <div class="titlepage"><div><div><h3 class="title">
  91 <a name="core.explicit_operator_bool.history"></a><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.history" title="History">History</a>
  92 </h3></div></div></div>
  93 <h5>
  94 <a name="core.explicit_operator_bool.history.h0"></a>
  95         <span class="phrase"><a name="core.explicit_operator_bool.history.boost_1_56"></a></span><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.history.boost_1_56">boost
  96         1.56</a>
  97       </h5>
  98 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  99 <li class="listitem">
 100             Added new macros <code class="computeroutput"><span class="identifier">BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT</span></code>
 101             and <code class="computeroutput"><span class="identifier">BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL</span></code>
 102             to define <code class="computeroutput"><span class="keyword">noexcept</span></code> and
 103             <code class="computeroutput"><span class="keyword">constexpr</span></code> operators.
 104           </li>
 105 <li class="listitem">
 106             The header moved to Boost.Core.
 107           </li>
 108 </ul></div>
 109 <h5>
 110 <a name="core.explicit_operator_bool.history.h1"></a>
 111         <span class="phrase"><a name="core.explicit_operator_bool.history.boost_1_55"></a></span><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.history.boost_1_55">boost
 112         1.55</a>
 113       </h5>
 114 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
 115             The macro was extracted from Boost.Log.
 116           </li></ul></div>
 117 </div>
 118 </div>
 119 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 120 <td align="left"></td>
 121 <td align="right"><div class="copyright-footer">Copyright &#169; 2014 Peter Dimov<br>Copyright &#169; 2014 Glen Fernandes<br>Copyright &#169; 2014 Andrey Semashev<p>
 122         Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost
 123         Software License, Version 1.0</a>.
 124       </p>
 125 </div></td>
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