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  27 <a name="boost_typetraits.user_defined"></a><a class="link" href="user_defined.html" title="User Defined Specializations">User Defined Specializations</a>
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  29 <p>
  30       Occationally the end user may need to provide their own specialization for
  31       one of the type traits - typically where intrinsic compiler support is required
  32       to implement a specific trait fully. These specializations should derive from
  33       boost::<a class="link" href="reference/integral_constant.html" title="integral_constant">true_type</a>
  34       or boost::<a class="link" href="reference/integral_constant.html" title="integral_constant">false_type</a>
  35       as appropriate:
  36     </p>
  37 <pre class="programlisting"><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">is_pod</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  38 <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">is_class</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  39 <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">is_union</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  40
  41 <span class="keyword">struct</span> <span class="identifier">my_pod</span><span class="special">{};</span>
  42 <span class="keyword">struct</span> <span class="identifier">my_union</span>
  43 <span class="special">{</span>
  44    <span class="keyword">char</span> <span class="identifier">c</span><span class="special">;</span>
  45    <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span>
  46 <span class="special">};</span>
  47
  48 <span class="keyword">namespace</span> <span class="identifier">boost</span>
  49 <span class="special">{</span>
  50    <span class="keyword">template</span><span class="special">&lt;&gt;</span>
  51    <span class="keyword">struct</span> <a class="link" href="reference/is_pod.html" title="is_pod">is_pod</a><span class="special">&lt;</span><span class="identifier">my_pod</span><span class="special">&gt;</span> <span class="special">:</span> <span class="keyword">public</span> <a class="link" href="reference/integral_constant.html" title="integral_constant">true_type</a><span class="special">{};</span>
  52
  53    <span class="keyword">template</span><span class="special">&lt;&gt;</span>
  54    <span class="keyword">struct</span> <a class="link" href="reference/is_pod.html" title="is_pod">is_pod</a><span class="special">&lt;</span><span class="identifier">my_union</span><span class="special">&gt;</span> <span class="special">:</span> <span class="keyword">public</span> <a class="link" href="reference/integral_constant.html" title="integral_constant">true_type</a><span class="special">{};</span>
  55
  56    <span class="keyword">template</span><span class="special">&lt;&gt;</span>
  57    <span class="keyword">struct</span> <a class="link" href="reference/is_union.html" title="is_union">is_union</a><span class="special">&lt;</span><span class="identifier">my_union</span><span class="special">&gt;</span> <span class="special">:</span> <span class="keyword">public</span> <a class="link" href="reference/integral_constant.html" title="integral_constant">true_type</a><span class="special">{};</span>
  58
  59    <span class="keyword">template</span><span class="special">&lt;&gt;</span>
  60    <span class="keyword">struct</span> <a class="link" href="reference/is_class.html" title="is_class">is_class</a><span class="special">&lt;</span><span class="identifier">my_union</span><span class="special">&gt;</span> <span class="special">:</span> <span class="keyword">public</span> <a class="link" href="reference/integral_constant.html" title="integral_constant">false_type</a><span class="special">{};</span>
  61 <span class="special">}</span>
  62 </pre>
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