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<title>Support for Compiler Intrinsics</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_typetraits.intrinsics"></a><a class="link" href="intrinsics.html" title="Support for Compiler Intrinsics">Support for Compiler Intrinsics</a>
</h2></div></div></div>
<p>
      There are some traits that can not be implemented within the current C++ language:
      to make these traits "just work" with user defined types, some kind
      of additional help from the compiler is required. Currently (April 2008) Visual
      C++ 8 and 9, GNU GCC 4.3 and MWCW 9 provide at least some of the the necessary
      intrinsics, and other compilers will no doubt follow in due course.
    </p>
<p>
      The Following traits classes always need compiler support to do the right thing
      for all types (but all have safe fallback positions if this support is unavailable):
    </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          <a class="link" href="reference/is_final.html" title="is_final">is_final</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/is_union.html" title="is_union">is_union</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/is_pod.html" title="is_pod">is_pod</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/is_nothrow_move_assignable.html" title="is_nothrow_move_assignable">is_nothrow_move_assignable</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/is_nothrow_move_constructible.html" title="is_nothrow_move_constructible">is_nothrow_move_constructible</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/has_trivial_constructor.html" title="has_trivial_constructor">has_trivial_constructor</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/has_trivial_copy.html" title="has_trivial_copy">has_trivial_copy</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/has_trivial_move_constructor.html" title="has_trivial_move_constructor">has_trivial_move_constructor</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/has_trivial_assign.html" title="has_trivial_assign">has_trivial_assign</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/has_trivial_move_assign.html" title="has_trivial_move_assign">has_trivial_move_assign</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/has_trivial_destructor.html" title="has_trivial_destructor">has_trivial_destructor</a>
        </li>
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          <a class="link" href="reference/has_nothrow_constructor.html" title="has_nothrow_constructor">has_nothrow_constructor</a>
        </li>
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          <a class="link" href="reference/has_nothrow_copy.html" title="has_nothrow_copy">has_nothrow_copy</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/has_nothrow_assign.html" title="has_nothrow_assign">has_nothrow_assign</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/has_virtual_destructor.html" title="has_virtual_destructor">has_virtual_destructor</a>
        </li>
</ul></div>
<p>
      The following traits classes can't be portably implemented in the C++ language,
      although in practice, the implementations do in fact do the right thing on
      all the compilers we know about:
    </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          <a class="link" href="reference/is_empty.html" title="is_empty">is_empty</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/is_polymorphic.html" title="is_polymorphic">is_polymorphic</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/is_virtual_base_of.html" title="is_virtual_base_of">is_virtual_base_of</a>
        </li>
</ul></div>
<p>
      The following traits classes are dependent on one or more of the above:
    </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          <a class="link" href="reference/is_class.html" title="is_class">is_class</a>
        </li>
<li class="listitem">
          <a class="link" href="reference/is_stateless.html" title="is_stateless">is_stateless</a>
        </li>
</ul></div>
<p>
      The hooks for compiler-intrinsic support are defined in <a href="../../../../../boost/type_traits/intrinsics.hpp" target="_top">boost/type_traits/intrinsics.hpp</a>,
      adding support for new compilers is simply a matter of defining one of more
      of the following macros:
    </p>
<div class="table">
<a name="boost_typetraits.intrinsics.macros_for_compiler_intrinsics"></a><p class="title"><b>Table&#160;1.9.&#160;Macros for Compiler Intrinsics</b></p>
<div class="table-contents"><table class="table" summary="Macros for Compiler Intrinsics">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
              <p>
                BOOST_ALIGNMENT_OF(T)
              </p>
            </th>
<th>
              <p>
                Should evaluate to the alignment requirements of type T
              </p>
            </th>
</tr></thead>
<tbody>
<tr>
<td>
              <p>
                BOOST_IS_ABSTRACT(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is an abstract type
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_BASE_OF(T,U)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is a base class of U
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_CLASS(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is a class type
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_CONVERTIBLE(T,U)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is convertible to U
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_EMPTY(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is an empty struct or union
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_ENUM(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true is T is an enum
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_FINAL(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is a class type declared with the final
                specifier
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_NOTHROW_MOVE_ASSIGN(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true T has a non-throwing move assign operator.
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_NOTHROW_MOVE_CONSTRUCT(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true T has a non-throwing move constructor.
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_POLYMORPHIC(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is a polymorphic type
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_POD(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is a POD type
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_IS_UNION(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T is a union type
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_NOTHROW_ASSIGN(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if <code class="computeroutput"><span class="identifier">T</span>
                <span class="identifier">t</span><span class="special">,</span>
                <span class="identifier">u</span><span class="special">;</span>
                <span class="identifier">t</span> <span class="special">=</span>
                <span class="identifier">u</span></code> can not throw
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_NOTHROW_CONSTRUCTOR(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if <code class="computeroutput"><span class="identifier">T</span>
                <span class="identifier">x</span><span class="special">;</span></code>
                can not throw
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_NOTHROW_COPY(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if <code class="computeroutput"><span class="identifier">T</span><span class="special">(</span><span class="identifier">t</span><span class="special">)</span></code> can not throw
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_TRIVIAL_ASSIGN(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T has a trivial assignment operator (and
                can therefore be replaced by a call to memcpy)
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_TRIVIAL_CONSTRUCTOR(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if the default constructor for T is trivial
                (i.e. has no effect)
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_TRIVIAL_COPY(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T has a trivial copy constructor (and
                can therefore be replaced by a call to memcpy)
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_TRIVIAL_DESTRUCTOR(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T has a trivial destructor (i.e. ~T()
                has no effect)
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_TRIVIAL_MOVE_CONSTRUCTOR(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T has a trivial move constructor (and
                can therefore be replaced by a call to memcpy)
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_TRIVIAL_MOVE_ASSIGN(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true if T has a trivial move assignment operator
                (and can therefore be replaced by a call to memcpy)
              </p>
            </td>
</tr>
<tr>
<td>
              <p>
                BOOST_HAS_VIRTUAL_DESTRUCTOR(T)
              </p>
            </td>
<td>
              <p>
                Should evaluate to true T has a virtual destructor
              </p>
            </td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break">
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2000, 2011 Adobe Systems Inc, David Abrahams,
      Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant,
      Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten
      Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven
      Watanabe<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
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