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<title>Categorizing a Type</title>
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<div class="section boost_typetraits_category_value_traits_primary">
<div class="titlepage"><div><div><h4 class="title">
<a name="boost_typetraits.category.value_traits.primary"></a><a class="link" href="primary.html" title="Categorizing a Type">Categorizing
a Type</a>
</h4></div></div></div>
<p>
These traits identify what "kind" of type some type <code class="computeroutput"><span class="identifier">T</span></code> is. These are split into two groups:
primary traits which are all mutually exclusive, and composite traits that
are compositions of one or more primary traits.
</p>
<p>
For any given type, exactly one primary type trait will inherit from <a class="link" href="../../reference/integral_constant.html" title="integral_constant">true_type</a>,
and all the others will inherit from <a class="link" href="../../reference/integral_constant.html" title="integral_constant">false_type</a>,
in other words these traits are mutually exclusive.
</p>
<p>
This means that <code class="computeroutput"><a class="link" href="../../reference/is_integral.html" title="is_integral">is_integral</a><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
and <code class="computeroutput"><a class="link" href="../../reference/is_floating_point.html" title="is_floating_point">is_floating_point</a><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
will only ever be true for built-in types; if you want to check for a user-defined
class type that behaves "as if" it is an integral or floating
point type, then use the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span>
<span class="keyword">template</span></code> instead.
</p>
<p>
<span class="bold"><strong>Synopsis:</strong></span>
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_array.html" title="is_array">is_array</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_class.html" title="is_class">is_class</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_complex.html" title="is_complex">is_complex</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_enum.html" title="is_enum">is_enum</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_floating_point.html" title="is_floating_point">is_floating_point</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_function.html" title="is_function">is_function</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_integral.html" title="is_integral">is_integral</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_member_function_pointer.html" title="is_member_function_pointer">is_member_function_pointer</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_member_object_pointer.html" title="is_member_object_pointer">is_member_object_pointer</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_pointer.html" title="is_pointer">is_pointer</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_lvalue_reference.html" title="is_lvalue_reference">is_lvalue_reference</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_rvalue_reference.html" title="is_rvalue_reference">is_rvalue_reference</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_union.html" title="is_union">is_union</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_void.html" title="is_void">is_void</a><span class="special">;</span>
</pre>
<p>
The following traits are made up of the union of one or more type categorizations.
A type may belong to more than one of these categories, in addition to
one of the primary categories.
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_arithmetic.html" title="is_arithmetic">is_arithmetic</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_compound.html" title="is_compound">is_compound</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_fundamental.html" title="is_fundamental">is_fundamental</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_member_pointer.html" title="is_member_pointer">is_member_pointer</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_object.html" title="is_object">is_object</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_reference.html" title="is_reference">is_reference</a><span class="special">;</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">struct</span> <a class="link" href="../../reference/is_scalar.html" title="is_scalar">is_scalar</a><span class="special">;</span>
</pre>
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