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- <h1><a class="toc-backref" href="./changes-in-boost-1-32-0.html#id67" name="numeric-metafunction">Numeric Metafunction Protocol/Infrastructure</a></h1>
- <p>The arithmetic, comparison and bitwise metafunctions are now
- <cite>polymorphic</cite>, and can operate on a variety of numeric types,
- including rational, fixed-point and complex numbers. They allow
- <cite>mixed arithmetic</cite>, meaning that you can perform an operation on
- arguments of different types, and the result will yield the
- largest/most general of the argument types. The infrastructure
- allows user-defined numeric types to be freely intermixed with
- predefined library types. See
- <a class="reference" href="../../test/numeric_ops.cpp" target="_top">libs/mpl/test/numeric_ops.cpp</a>
- for an illustrative example, and the <a class="reference" href="./reference-manual.html">reference manual</a> for
- the formal infrastructure specification.</p>
- <p>If you were using MPL numeric metafunctions on your own integral
- wrapper class similar to <tt class="literal"><span class="pre">mpl::int_</span></tt>, you can plug your class
- into the new infrastructure by extending it with the following
- member:</p>
- <pre class="literal-block">
- typedef mpl::integral_c_tag tag;
- </pre>
- <p>For example:</p>
- <table border="1" class="table">
- <colgroup>
- <col width="48%" />
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- <tr><th>Before</th>
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- <tr><td><pre class="first last literal-block">
- template< int n > struct my_int
- {
- static int const value = n;
- typedef my_int type;
- };
- </pre>
- </td>
- <td><pre class="first last literal-block">
- template< int n > struct my_int
- {
- <strong>typedef mpl::integral_c_tag tag;</strong>
- static int const value = n;
- typedef my_int type;
- };
- </pre>
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