ceph/src/boost/libs/mpl/doc/tutorial/numeric-metafunction.html

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