projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Metafunctions/Composition and Argument Binding//lambda |20 |
| 2 | ||
| 3 | lambda | |
| 4 | ====== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename X | |
| 13 | , typename Tag = |unspecified| | |
| 14 | > | |
| 15 | struct lambda | |
| 16 | { | |
| 17 | typedef |unspecified| type; | |
| 18 | }; | |
| 19 | ||
| 20 | ||
| 21 | ||
| 22 | Description | |
| 23 | ----------- | |
| 24 | ||
| 25 | If ``X`` is a |placeholder expression|, transforms ``X`` into a corresponding | |
| 26 | |Metafunction Class|, otherwise ``X`` is returned unchanged. | |
| 27 | ||
| 28 | ||
| 29 | Header | |
| 30 | ------ | |
| 31 | ||
| 32 | .. parsed-literal:: | |
| 33 | ||
| 34 | #include <boost/mpl/lambda.hpp> | |
| 35 | ||
| 36 | ||
| 37 | Parameters | |
| 38 | ---------- | |
| 39 | ||
| 40 | +---------------+-----------------------+-----------------------------------------------+ | |
| 41 | | Parameter | Requirement | Description | | |
| 42 | +===============+=======================+===============================================+ | |
| 43 | | ``X`` | Any type | An expression to transform. | | |
| 44 | +---------------+-----------------------+-----------------------------------------------+ | |
| 45 | | ``Tag`` | Any type | A tag determining transform semantics. | | |
| 46 | +---------------+-----------------------+-----------------------------------------------+ | |
| 47 | ||
| 48 | Expression semantics | |
| 49 | -------------------- | |
| 50 | ||
| 51 | For arbitrary types ``x`` and ``tag``: | |
| 52 | ||
| 53 | ||
| 54 | .. parsed-literal:: | |
| 55 | ||
| 56 | typedef lambda<x>::type f; | |
| 57 | ||
| 58 | :Return type: | |
| 59 | |Metafunction Class|. | |
| 60 | ||
| 61 | :Semantics: | |
| 62 | If ``x`` is a |placeholder expression| in a general form ``X<a1,...an>``, where | |
| 63 | ``X`` is a class template and ``a1``,... ``an`` are arbitrary types, equivalent | |
| 64 | to | |
| 65 | ||
| 66 | .. parsed-literal:: | |
| 67 | ||
| 68 | typedef protect< bind< | |
| 69 | quote\ *n*\ <X> | |
| 70 | , lambda<a1>::type,\ |...| lambda<a\ *n*\ >::type | |
| 71 | > > f; | |
| 72 | ||
| 73 | otherwise, ``f`` is identical to ``x``. | |
| 74 | ||
| 75 | .. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
| 76 | ||
| 77 | .. parsed-literal:: | |
| 78 | ||
| 79 | typedef lambda<x,tag>::type f; | |
| 80 | ||
| 81 | :Return type: | |
| 82 | |Metafunction Class|. | |
| 83 | ||
| 84 | :Semantics: | |
| 85 | If ``x`` is a |placeholder expression| in a general form ``X<a1,...an>``, where | |
| 86 | ``X`` is a class template and ``a1``,... ``an`` are arbitrary types, equivalent | |
| 87 | to | |
| 88 | ||
| 89 | .. parsed-literal:: | |
| 90 | ||
| 91 | typedef protect< bind< | |
| 92 | quote\ *n*\ <X,tag> | |
| 93 | , lambda<a1,tag>::type,\ |...| lambda<a\ *n*\ ,tag>::type | |
| 94 | > > f; | |
| 95 | ||
| 96 | otherwise, ``f`` is identical to ``x``. | |
| 97 | ||
| 98 | ||
| 99 | Example | |
| 100 | ------- | |
| 101 | ||
| 102 | .. parsed-literal:: | |
| 103 | ||
| 104 | template< typename N1, typename N2 > struct int_plus | |
| 105 | : int_<( N1::value + N2::value )> | |
| 106 | { | |
| 107 | }; | |
| 108 | ||
| 109 | typedef lambda< int_plus<_1, int_<42> > >::type f1; | |
| 110 | typedef bind< quote\ ``2``\ <int_plus>, _1, int_<42> > f2; | |
| 111 | ||
| 112 | typedef f1::apply<42>::type r1; | |
| 113 | typedef f2::apply<42>::type r2; | |
| 114 | ||
| 115 | BOOST_MPL_ASSERT_RELATION( r1::value, ==, 84 ); | |
| 116 | BOOST_MPL_ASSERT_RELATION( r2::value, ==, 84 ); | |
| 117 | ||
| 118 | ||
| 119 | See also | |
| 120 | -------- | |
| 121 | ||
| 122 | |Composition and Argument Binding|, |Invocation|, |Placeholders|, |bind|, |quote|, |protect|, |apply| | |
| 123 | ||
| 124 | ||
| 125 |