ceph/src/boost/libs/mpl/doc/src/refmanual/numeric_cast.rst

   1 .. Metafunctions/Miscellaneous//numeric_cast |50
   2
   3 numeric_cast
   4 ============
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename SourceTag
  13         , typename TargetTag
  14         >
  15     struct numeric_cast;
  16
  17
  18 Description
  19 -----------
  20
  21 Each ``numeric_cast`` specialization is a user-specialized unary |Metafunction Class|
  22 providing a conversion between two numeric types.
  23
  24
  25 Header
  26 ------
  27
  28 .. parsed-literal::
  29
  30     #include <boost/mpl/numeric_cast.hpp>
  31
  32
  33 Parameters
  34 ----------
  35
  36 +---------------+---------------------------+-----------------------------------------------+
  37 | Parameter     | Requirement               | Description                                   |
  38 +===============+===========================+===============================================+
  39 | ``SourceTag`` | |Integral Constant|       | A tag for the conversion's source type.       |
  40 +---------------+---------------------------+-----------------------------------------------+
  41 | ``TargetTag`` | |Integral Constant|       | A tag for the conversion's destination type.  |
  42 +---------------+---------------------------+-----------------------------------------------+
  43
  44
  45 Expression semantics
  46 --------------------
  47
  48 If ``x`` and ``y`` are two numeric types, ``x`` is convertible to ``y``, and
  49 ``x_tag`` and ``y_tag`` are the types' corresponding |Integral Constant| tags:
  50
  51
  52 .. parsed-literal::
  53
  54     typedef apply_wrap\ ``2``\< numeric_cast<x_tag,y_tag>,x >::type  r;
  55
  56 :Return type:
  57     A type.
  58
  59 :Semantics:
  60     ``r`` is a value of ``x`` converted to the type of ``y``.
  61
  62
  63 Complexity
  64 ----------
  65
  66 Unspecified.
  67
  68
  69 Example
  70 -------
  71
  72 .. parsed-literal::
  73
  74     struct complex_tag : int_<10> {};
  75
  76     template< typename Re, typename Im > struct complex
  77     {
  78         typedef complex_tag tag;
  79         typedef complex type;
  80         typedef Re real;
  81         typedef Im imag;
  82     };
  83
  84     template< typename C > struct real : C::real {};
  85     template< typename C > struct imag : C::imag {};
  86
  87     namespace boost { namespace mpl {
  88
  89     template<> struct numeric_cast< integral_c_tag,complex_tag >
  90     {
  91         template< typename N > struct apply
  92             : complex< N, integral_c< typename N::value_type, 0 > >
  93         {
  94         };
  95     };
  96
  97     template<>
  98     struct plus_impl< complex_tag,complex_tag >
  99     {
 100         template< typename N1, typename N2 > struct apply
 101             : complex<
 102                   plus< typename N1::real, typename N2::real >
 103                 , plus< typename N1::imag, typename N2::imag >
 104                 >
 105         {
 106         };
 107     };
 108
 109     }}
 110
 111     typedef int_<2> i;
 112     typedef complex< int_<5>, int_<-1> > c1;
 113     typedef complex< int_<-5>, int_<1> > c2;
 114
 115     typedef plus<c1,i> r4;
 116     BOOST_MPL_ASSERT_RELATION( real<r4>::value, ==, 7 );
 117     BOOST_MPL_ASSERT_RELATION( imag<r4>::value, ==, -1 );
 118
 119     typedef plus<i,c2> r5;
 120     BOOST_MPL_ASSERT_RELATION( real<r5>::value, ==, -3 );
 121     BOOST_MPL_ASSERT_RELATION( imag<r5>::value, ==, 1 );
 122
 123
 124 See also
 125 --------
 126
 127 |Metafunctions|, |Numeric Metafunction|, |plus|, |minus|, |times|
 128
 129
 130 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 131    Distributed under the Boost Software License, Version 1.0. (See accompanying
 132    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)