projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Metafunctions/Invocation//apply_wrap |20 |
| 2 | ||
| 3 | apply_wrap | |
| 4 | ========== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename F | |
| 13 | > | |
| 14 | struct apply_wrap0 | |
| 15 | { | |
| 16 | typedef |unspecified| type; | |
| 17 | }; | |
| 18 | ||
| 19 | template< | |
| 20 | typename F, typename A1 | |
| 21 | > | |
| 22 | struct apply_wrap1 | |
| 23 | { | |
| 24 | typedef |unspecified| type; | |
| 25 | }; | |
| 26 | ||
| 27 | |...| | |
| 28 | ||
| 29 | template< | |
| 30 | typename F, typename A1,\ |...| typename An | |
| 31 | > | |
| 32 | struct apply_wrap\ *n* | |
| 33 | { | |
| 34 | typedef |unspecified| type; | |
| 35 | }; | |
| 36 | ||
| 37 | ||
| 38 | ||
| 39 | Description | |
| 40 | ----------- | |
| 41 | ||
| 42 | Invokes a |Metafunction Class| ``F`` with arguments ``A1``,... ``An``. | |
| 43 | ||
| 44 | In essence, ``apply_wrap`` forms are nothing more than syntactic wrappers around | |
| 45 | ``F::apply<A1,... An>::type`` / ``F::apply::type`` expressions (hence the name). | |
| 46 | They provide a more concise notation and higher portability than their | |
| 47 | underlaying constructs at the cost of an extra template instantiation. | |
| 48 | ||
| 49 | ||
| 50 | Header | |
| 51 | ------ | |
| 52 | ||
| 53 | .. parsed-literal:: | |
| 54 | ||
| 55 | #include <boost/mpl/apply_wrap.hpp> | |
| 56 | ||
| 57 | ||
| 58 | Parameters | |
| 59 | ---------- | |
| 60 | ||
| 61 | +---------------+-----------------------------------+-----------------------------------------------+ | |
| 62 | | Parameter | Requirement | Description | | |
| 63 | +===============+===================================+===============================================+ | |
| 64 | | ``F`` | |Metafunction Class| | A metafunction class to invoke. | | |
| 65 | +---------------+-----------------------------------+-----------------------------------------------+ | |
| 66 | | |A1...An| | Any type | Invocation arguments. | | |
| 67 | +---------------+-----------------------------------+-----------------------------------------------+ | |
| 68 | ||
| 69 | ||
| 70 | Expression semantics | |
| 71 | -------------------- | |
| 72 | ||
| 73 | For any |Metafunction Class| ``f`` and arbitrary types |a1...an|: | |
| 74 | ||
| 75 | ||
| 76 | .. parsed-literal:: | |
| 77 | ||
| 78 | typedef apply_wrap\ *n*\ <f,a1,\ |...|\ an>::type t; | |
| 79 | ||
| 80 | :Return type: | |
| 81 | Any type. | |
| 82 | ||
| 83 | :Semantics: | |
| 84 | If ``n > 0``, equivalent to ``typedef f::apply<a1,... an>::type t;``, | |
| 85 | otherwise equivalent to either ``typedef f::apply::type t;`` or | |
| 86 | ``typedef f::apply<>::type t;`` depending on whether ``f::apply`` is | |
| 87 | a class or a class template. | |
| 88 | ||
| 89 | ||
| 90 | Example | |
| 91 | ------- | |
| 92 | ||
| 93 | .. parsed-literal:: | |
| 94 | ||
| 95 | struct f0 | |
| 96 | { | |
| 97 | template< typename T = int > struct apply | |
| 98 | { | |
| 99 | typedef char type; | |
| 100 | }; | |
| 101 | }; | |
| 102 | ||
| 103 | struct g0 | |
| 104 | { | |
| 105 | struct apply { typedef char type; }; | |
| 106 | }; | |
| 107 | ||
| 108 | struct f2 | |
| 109 | { | |
| 110 | template< typename T1, typename T2 > struct apply | |
| 111 | { | |
| 112 | typedef T2 type; | |
| 113 | }; | |
| 114 | }; | |
| 115 | ||
| 116 | ||
| 117 | typedef apply_wrap\ ``0``\ < f0 >::type r1; | |
| 118 | typedef apply_wrap\ ``0``\ < g0 >::type r2; | |
| 119 | typedef apply_wrap\ ``2``\ < f2,int,char >::type r3; | |
| 120 | ||
| 121 | BOOST_MPL_ASSERT(( is_same<r1,char> )); | |
| 122 | BOOST_MPL_ASSERT(( is_same<r2,char> )); | |
| 123 | BOOST_MPL_ASSERT(( is_same<r3,char> )); | |
| 124 | ||
| 125 | ||
| 126 | See also | |
| 127 | -------- | |
| 128 | ||
| 129 | |Metafunctions|, |Invocation|, |apply|, |lambda|, |quote|, |bind|, |protect| | |
| 130 | ||
| 131 | ||
| 132 |