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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_typetraits.reference.is_base_of"></a><a class="link" href="is_base_of.html" title="is_base_of">is_base_of</a>
  28 </h3></div></div></div>
  29 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Base</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Derived</span><span class="special">&gt;</span>
  30 <span class="keyword">struct</span> <span class="identifier">is_base_of</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span>
  31 </pre>
  32 <p>
  33         <span class="bold"><strong>Inherits:</strong></span> If Base is base class of type
  34         Derived or if both types are the same class type then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
  35         otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
  36       </p>
  37 <p>
  38         This template will detect non-public base classes, and ambiguous base classes.
  39         It also detects indirect base classes - which is to say <a class="link" href="is_base_of.html" title="is_base_of">is_base_of</a>&lt;B,
  40         D&gt; inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>
  41         if B is located anywhere in the inheritance tree of D.
  42       </p>
  43 <p>
  44         Note that <code class="computeroutput"><span class="identifier">is_base_of</span><span class="special">&lt;</span><span class="identifier">X</span><span class="special">,</span><span class="identifier">X</span><span class="special">&gt;</span></code> will inherit from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>
  45         if X is a class type. This is a change in behaviour from Boost-1.39.0 in
  46         order to track the emerging C++0x standard.
  47       </p>
  48 <p>
  49         Types <code class="computeroutput"><span class="identifier">Base</span></code> and <code class="computeroutput"><span class="identifier">Derived</span></code> must not be incomplete types.
  50       </p>
  51 <p>
  52         <span class="bold"><strong>C++ Standard Reference:</strong></span> 10.
  53       </p>
  54 <p>
  55         <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
  56         <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_base_of</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  57         or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  58       </p>
  59 <p>
  60         <span class="bold"><strong>Compiler Compatibility:</strong></span> If the compiler
  61         does not support partial-specialization of class templates, then this template
  62         can not be used with function types. There are some older compilers which
  63         will produce compiler errors if <code class="computeroutput"><span class="identifier">Base</span></code>
  64         is a private base class of <code class="computeroutput"><span class="identifier">Derived</span></code>,
  65         or if <code class="computeroutput"><span class="identifier">Base</span></code> is an ambiguous
  66         base of <code class="computeroutput"><span class="identifier">Derived</span></code>. These compilers
  67         include Borland C++, older versions of Sun Forte C++, Digital Mars C++, and
  68         older versions of EDG based compilers.
  69       </p>
  70 <p>
  71         <span class="bold"><strong>Examples:</strong></span>
  72       </p>
  73 <div class="blockquote"><blockquote class="blockquote"><p>
  74           Given: <code class="computeroutput"> <span class="keyword">class</span> <span class="identifier">Base</span><span class="special">{};</span> <span class="keyword">class</span> <span class="identifier">Derived</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">Base</span><span class="special">{};</span></code>
  75         </p></blockquote></div>
  76 <div class="blockquote"><blockquote class="blockquote"><p>
  77           <code class="computeroutput"><span class="identifier">is_base_of</span><span class="special">&lt;</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">&gt;</span></code>
  78           inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
  79         </p></blockquote></div>
  80 <div class="blockquote"><blockquote class="blockquote"><p>
  81           <code class="computeroutput"><span class="identifier">is_base_of</span><span class="special">&lt;</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">&gt;::</span><span class="identifier">type</span></code> is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
  82         </p></blockquote></div>
  83 <div class="blockquote"><blockquote class="blockquote"><p>
  84           <code class="computeroutput"><span class="identifier">is_base_of</span><span class="special">&lt;</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
  85           that evaluates to <span class="emphasis"><em>true</em></span>.
  86         </p></blockquote></div>
  87 <div class="blockquote"><blockquote class="blockquote"><p>
  88           <code class="computeroutput"><span class="identifier">is_base_of</span><span class="special">&lt;</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Base</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
  89           that evaluates to <span class="emphasis"><em>true</em></span>: a class is regarded as it's
  90           own base.
  91         </p></blockquote></div>
  92 <div class="blockquote"><blockquote class="blockquote"><p>
  93           <code class="computeroutput"><span class="identifier">is_base_of</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value_type</span></code>
  94           is the type <code class="computeroutput"><span class="keyword">bool</span></code>.
  95         </p></blockquote></div>
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