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| <div class="section" id="numeric-metafunction"> |
| <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="http://cvs.sourceforge.net/viewcvs.py/boost/boost/libs/mpl/test/numeric_ops.cpp?view=markup" target="_top">http://cvs.sourceforge.net/viewcvs.py/boost/boost/libs/mpl/test/numeric_ops.cpp?view=markup</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> |
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| 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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