projects / ceph.git / blame
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|---|---|---|
| 7c673cae FG |
1 | .. Metafunctions/Composition and Argument Binding//bind |30 |
| 2 | ||
| 3 | bind | |
| 4 | ==== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename F | |
| 13 | > | |
| 14 | struct bind0 | |
| 15 | { | |
| 16 | // |unspecified| | |
| 17 | // |...| | |
| 18 | }; | |
| 19 | ||
| 20 | template< | |
| 21 | typename F, typename A1 | |
| 22 | > | |
| 23 | struct bind1 | |
| 24 | { | |
| 25 | // |unspecified| | |
| 26 | // |...| | |
| 27 | }; | |
| 28 | ||
| 29 | |...| | |
| 30 | ||
| 31 | template< | |
| 32 | typename F, typename A1,\ |...| typename An | |
| 33 | > | |
| 34 | struct bind\ *n* | |
| 35 | { | |
| 36 | // |unspecified| | |
| 37 | // |...| | |
| 38 | }; | |
| 39 | ||
| 40 | template< | |
| 41 | typename F | |
| 42 | , typename A1 = |unspecified| | |
| 43 | |...| | |
| 44 | , typename An = |unspecified| | |
| 45 | > | |
| 46 | struct bind | |
| 47 | { | |
| 48 | // |unspecified| | |
| 49 | // |...| | |
| 50 | }; | |
| 51 | ||
| 52 | ||
| 53 | Description | |
| 54 | ----------- | |
| 55 | ||
| 56 | ``bind`` is a higher-order primitive for |Metafunction Class| composition | |
| 57 | and argument binding. In essence, it's a compile-time counterpart of | |
| 58 | the similar run-time functionality provided by |Boost.Bind| and |Boost.Lambda| | |
| 59 | libraries. | |
| 60 | ||
| 61 | ||
| 62 | Header | |
| 63 | ------ | |
| 64 | ||
| 65 | .. parsed-literal:: | |
| 66 | ||
| 67 | #include <boost/mpl/bind.hpp> | |
| 68 | ||
| 69 | ||
| 70 | Model of | |
| 71 | -------- | |
| 72 | ||
| 73 | |Metafunction Class| | |
| 74 | ||
| 75 | ||
| 76 | Parameters | |
| 77 | ---------- | |
| 78 | ||
| 79 | +---------------+-----------------------------------+-----------------------------------------------+ | |
| 80 | | Parameter | Requirement | Description | | |
| 81 | +===============+===================================+===============================================+ | |
| 82 | | ``F`` | |Metafunction Class| | An metafunction class to perform binding on. | | |
| 83 | +---------------+-----------------------------------+-----------------------------------------------+ | |
| 84 | | |A1...An| | Any type | Arguments to bind. | | |
| 85 | +---------------+-----------------------------------+-----------------------------------------------+ | |
| 86 | ||
| 87 | ||
| 88 | Expression semantics | |
| 89 | -------------------- | |
| 90 | ||
| 91 | For any |Metafunction Class| ``f`` and arbitrary types |a1...an|: | |
| 92 | ||
| 93 | .. parsed-literal:: | |
| 94 | ||
| 95 | typedef bind<f,a1,...a\ *n*\ > g; | |
| 96 | typedef bind\ *n*\ <f,a1,...a\ *n*\ > g; | |
| 97 | ||
| 98 | :Return type: | |
| 99 | |Metafunction Class| | |
| 100 | ||
| 101 | .. _`bind semantics`: | |
| 102 | ||
| 103 | :Semantics: | |
| 104 | Equivalent to | |
| 105 | ||
| 106 | .. parsed-literal:: | |
| 107 | ||
| 108 | struct g | |
| 109 | { | |
| 110 | template< | |
| 111 | typename U1 = |unspecified| | |
| 112 | |...| | |
| 113 | , typename U\ *n* = |unspecified| | |
| 114 | > | |
| 115 | struct apply | |
| 116 | : apply_wrap\ *n*\ < | |
| 117 | typename h0<f,U1,\ |...|\ U\ *n*>::type | |
| 118 | , typename h1<a1,U1,\ |...|\ U\ *n*>::type | |
| 119 | |...| | |
| 120 | , typename h\ *n*\ <a\ *n*\ ,U1,\ |...|\ U\ *n*>::type | |
| 121 | > | |
| 122 | { | |
| 123 | }; | |
| 124 | }; | |
| 125 | ||
| 126 | where ``h``\ *k* is equivalent to | |
| 127 | ||
| 128 | .. parsed-literal:: | |
| 129 | ||
| 130 | template< typename X, typename U1,\ |...| typename U\ *n* > struct h\ *k* | |
| 131 | : apply_wrap\ *n*\ <X,U1,\ |...|\ U\ *n*> | |
| 132 | { | |
| 133 | }; | |
| 134 | ||
| 135 | if ``f`` or ``a``\ *k* is a |bind expression| or a |placeholder|, and | |
| 136 | ||
| 137 | .. parsed-literal:: | |
| 138 | ||
| 139 | template< typename X, typename U1,\ |...| typename U\ *n* > struct h\ *k* | |
| 140 | { | |
| 141 | typedef X type; | |
| 142 | }; | |
| 143 | ||
| 144 | otherwise. |Note:| Every ``n``\th appearance of the `unnamed placeholder`__ | |
| 145 | in the ``bind<f,a1,...an>`` specialization is replaced with the corresponding | |
| 146 | numbered placeholder ``_``\ *n* |-- end note| | |
| 147 | ||
| 148 | __ `Placeholders`_ | |
| 149 | ||
| 150 | ||
| 151 | Example | |
| 152 | ------- | |
| 153 | ||
| 154 | .. parsed-literal:: | |
| 155 | ||
| 156 | struct f1 | |
| 157 | { | |
| 158 | template< typename T1 > struct apply | |
| 159 | { | |
| 160 | typedef T1 type; | |
| 161 | }; | |
| 162 | }; | |
| 163 | ||
| 164 | struct f5 | |
| 165 | { | |
| 166 | template< typename T1, typename T2, typename T3, typename T4, typename T5 > | |
| 167 | struct apply | |
| 168 | { | |
| 169 | typedef T5 type; | |
| 170 | }; | |
| 171 | }; | |
| 172 | ||
| 173 | typedef apply_wrap\ ``1``\< | |
| 174 | bind\ ``1``\<f1,_1> | |
| 175 | , int | |
| 176 | >::type r11; | |
| 177 | ||
| 178 | typedef apply_wrap\ ``5``\< | |
| 179 | bind\ ``1``\<f1,_5> | |
| 180 | , void,void,void,void,int | |
| 181 | >::type r12; | |
| 182 | ||
| 183 | BOOST_MPL_ASSERT(( is_same<r11,int> )); | |
| 184 | BOOST_MPL_ASSERT(( is_same<r12,int> )); | |
| 185 | ||
| 186 | typedef apply_wrap\ ``5``\< | |
| 187 | bind\ ``5``\<f5,_1,_2,_3,_4,_5> | |
| 188 | , void,void,void,void,int | |
| 189 | >::type r51; | |
| 190 | ||
| 191 | typedef apply_wrap\ ``5``\< | |
| 192 | bind\ ``5``\<f5,_5,_4,_3,_2,_1> | |
| 193 | , int,void,void,void,void | |
| 194 | >::type r52; | |
| 195 | ||
| 196 | BOOST_MPL_ASSERT(( is_same<r51,int> )); | |
| 197 | BOOST_MPL_ASSERT(( is_same<r52,int> )); | |
| 198 | ||
| 199 | ||
| 200 | See also | |
| 201 | -------- | |
| 202 | ||
| 203 | |Composition and Argument Binding|, |Invocation|, |Placeholders|, |lambda|, |quote|, | |
| 204 | |protect|, |apply|, |apply_wrap| | |
| 205 | ||
| 206 | ||
| 207 |