projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Metafunctions/Concepts//Numeric Metafunction |60 |
| 2 | ||
| 3 | Numeric Metafunction | |
| 4 | ==================== | |
| 5 | ||
| 6 | Description | |
| 7 | ----------- | |
| 8 | ||
| 9 | A |Numeric Metafunction| is a |tag dispatched metafunction| that provides | |
| 10 | a built-in infrastructure for easy implementation of mixed-type operations. | |
| 11 | ||
| 12 | ||
| 13 | Expression requirements | |
| 14 | ----------------------- | |
| 15 | ||
| 16 | |In the following table...| ``op`` is a placeholder token for the actual | |
| 17 | |Numeric Metafunction|'s name, and ``x``, ``y`` and |x1...xn| are | |
| 18 | arbitrary numeric types. | |
| 19 | ||
| 20 | +-------------------------------------------+-----------------------+---------------------------+ | |
| 21 | | Expression | Type | Complexity | | |
| 22 | +===========================================+=======================+===========================+ | |
| 23 | |``op_tag<x>::type`` | |Integral Constant| | Amortized constant time. | | |
| 24 | +-------------------------------------------+-----------------------+---------------------------+ | |
| 25 | | .. parsed-literal:: | Any type | Unspecified. | | |
| 26 | | | | | | |
| 27 | | op_impl< | | | | |
| 28 | | op_tag<x>::type | | | | |
| 29 | | , op_tag<y>::type | | | | |
| 30 | | >::apply<x,y>::type | | | | |
| 31 | +-------------------------------------------+-----------------------+---------------------------+ | |
| 32 | |``op<``\ |x1...xn|\ ``>::type`` | Any type | Unspecified. | | |
| 33 | +-------------------------------------------+-----------------------+---------------------------+ | |
| 34 | ||
| 35 | ||
| 36 | Expression semantics | |
| 37 | -------------------- | |
| 38 | ||
| 39 | .. parsed-literal:: | |
| 40 | ||
| 41 | typedef op_tag<x>::type tag; | |
| 42 | ||
| 43 | :Semantics: | |
| 44 | ``tag`` is a tag type for ``x`` for ``op``. | |
| 45 | ``tag::value`` is ``x``\ 's *conversion rank*. | |
| 46 | ||
| 47 | ||
| 48 | .. .......................................................................... | |
| 49 | ||
| 50 | .. parsed-literal:: | |
| 51 | ||
| 52 | typedef op_impl< | |
| 53 | op_tag<x>::type | |
| 54 | , op_tag<y>::type | |
| 55 | >::apply<x,y>::type r; | |
| 56 | ||
| 57 | :Semantics: | |
| 58 | ``r`` is the result of ``op`` application on arguments ``x`` | |
| 59 | and ``y``. | |
| 60 | ||
| 61 | ||
| 62 | .. .......................................................................... | |
| 63 | ||
| 64 | .. parsed-literal:: | |
| 65 | ||
| 66 | typedef op<\ |x1...xn|\ >::type r; | |
| 67 | ||
| 68 | :Semantics: | |
| 69 | ``r`` is the result of ``op`` application on arguments |x1...xn|. | |
| 70 | ||
| 71 | ||
| 72 | ||
| 73 | ||
| 74 | Example | |
| 75 | ------- | |
| 76 | ||
| 77 | .. parsed-literal:: | |
| 78 | ||
| 79 | ||
| 80 | struct complex_tag : int_<10> {}; | |
| 81 | ||
| 82 | template< typename Re, typename Im > struct complex | |
| 83 | { | |
| 84 | typedef complex_tag tag; | |
| 85 | typedef complex type; | |
| 86 | typedef Re real; | |
| 87 | typedef Im imag; | |
| 88 | }; | |
| 89 | ||
| 90 | template< typename C > struct real : C::real {}; | |
| 91 | template< typename C > struct imag : C::imag {}; | |
| 92 | ||
| 93 | namespace boost { namespace mpl { | |
| 94 | ||
| 95 | template<> | |
| 96 | struct plus_impl< complex_tag,complex_tag > | |
| 97 | { | |
| 98 | template< typename N1, typename N2 > struct apply | |
| 99 | : complex< | |
| 100 | plus< typename N1::real, typename N2::real > | |
| 101 | , plus< typename N1::imag, typename N2::imag > | |
| 102 | > | |
| 103 | { | |
| 104 | }; | |
| 105 | }; | |
| 106 | ||
| 107 | }} | |
| 108 | ||
| 109 | typedef complex< int_<5>, int_<-1> > c1; | |
| 110 | typedef complex< int_<-5>, int_<1> > c2; | |
| 111 | ||
| 112 | typedef plus<c1,c2> r1; | |
| 113 | BOOST_MPL_ASSERT_RELATION( real<r1>::value, ==, 0 ); | |
| 114 | BOOST_MPL_ASSERT_RELATION( imag<r1>::value, ==, 0 ); | |
| 115 | ||
| 116 | typedef plus<c1,c1> r2; | |
| 117 | BOOST_MPL_ASSERT_RELATION( real<r2>::value, ==, 10 ); | |
| 118 | BOOST_MPL_ASSERT_RELATION( imag<r2>::value, ==, -2 ); | |
| 119 | ||
| 120 | typedef plus<c2,c2> r3; | |
| 121 | BOOST_MPL_ASSERT_RELATION( real<r3>::value, ==, -10 ); | |
| 122 | BOOST_MPL_ASSERT_RELATION( imag<r3>::value, ==, 2 ); | |
| 123 | ||
| 124 | ||
| 125 | ||
| 126 | Models | |
| 127 | ------ | |
| 128 | ||
| 129 | * |plus| | |
| 130 | * |minus| | |
| 131 | * |times| | |
| 132 | * |divides| | |
| 133 | ||
| 134 | ||
| 135 | See also | |
| 136 | -------- | |
| 137 | ||
| 138 | |Tag Dispatched Metafunction|, |Metafunctions|, |numeric_cast| | |
| 139 | ||
| 140 | ||
| 141 |