projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
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 |