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| 7 | <title>THE BOOST MPL LIBRARY: Numeric Metafunction Protocol/Infrastructure</title> |
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| 13 | </tr></table><div class="header-separator"></div> |
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| 14 | <div class="section" id="numeric-metafunction"> |
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| 15 | <h1><a class="toc-backref" href="./changes-in-boost-1-32-0.html#id67" name="numeric-metafunction">Numeric Metafunction Protocol/Infrastructure</a></h1> |
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| 16 | <p>The arithmetic, comparison and bitwise metafunctions are now |
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| 17 | <cite>polymorphic</cite>, and can operate on a variety of numeric types, |
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| 18 | including rational, fixed-point and complex numbers. They allow |
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| 19 | <cite>mixed arithmetic</cite>, meaning that you can perform an operation on |
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| 20 | arguments of different types, and the result will yeild the |
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| 21 | largest/most general of the argument types. The infrastructure |
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| 22 | allows user-defined numeric types to be freely intermixed with |
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| 23 | predefined library types. See |
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| 24 | <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> |
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| 25 | for an illustrative example, and the <a class="reference" href="./reference-manual.html">reference manual</a> for |
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| 26 | the formal infrastructure specification.</p> |
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| 27 | <p>If you were using MPL numeric metafunctions on your own integral |
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| 28 | wrapper class similar to <tt class="literal"><span class="pre">mpl::int_</span></tt>, you can plug your class |
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| 29 | into the new infrustructure by extending it with the following |
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| 30 | member:</p> |
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| 31 | <pre class="literal-block"> |
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| 32 | typedef mpl::integral_c_tag tag; |
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| 33 | </pre> |
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| 34 | <p>For example:</p> |
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| 35 | <table border="1" class="table"> |
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| 37 | <col width="48%" /> |
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| 38 | <col width="52%" /> |
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| 41 | <tr><th>Before</th> |
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| 44 | </thead> |
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| 45 | <tbody valign="top"> |
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| 46 | <tr><td><pre class="first last literal-block"> |
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| 47 | template< int n > struct my_int |
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| 48 | { |
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| 49 | static int const value = n; |
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| 50 | typedef my_int type; |
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| 51 | }; |
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| 52 | </pre> |
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| 53 | </td> |
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| 54 | <td><pre class="first last literal-block"> |
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| 55 | template< int n > struct my_int |
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| 56 | { |
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| 57 | <strong>typedef mpl::integral_c_tag tag;</strong> |
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| 58 | static int const value = n; |
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| 59 | typedef my_int type; |
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| 60 | }; |
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| 61 | </pre> |
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| 62 | </td> |
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| 63 | </tr> |
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