projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Metafunctions/Miscellaneous//always |20 |
| 2 | ||
| 3 | always | |
| 4 | ====== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename X | |
| 13 | > | |
| 14 | struct always | |
| 15 | { | |
| 16 | // |unspecified| | |
| 17 | // |...| | |
| 18 | }; | |
| 19 | ||
| 20 | ||
| 21 | Description | |
| 22 | ----------- | |
| 23 | ||
| 24 | ``always<X>`` specialization is a variadic |Metafunction Class| always returning the | |
| 25 | same type, ``X``, regardless of the number and types of passed arguments. | |
| 26 | ||
| 27 | ||
| 28 | Header | |
| 29 | ------ | |
| 30 | ||
| 31 | .. parsed-literal:: | |
| 32 | ||
| 33 | #include <boost/mpl/always.hpp> | |
| 34 | ||
| 35 | Model of | |
| 36 | -------- | |
| 37 | ||
| 38 | |Metafunction Class| | |
| 39 | ||
| 40 | ||
| 41 | Parameters | |
| 42 | ---------- | |
| 43 | ||
| 44 | +---------------+-------------------+-----------------------------------+ | |
| 45 | | Parameter | Requirement | Description | | |
| 46 | +===============+===================+===================================+ | |
| 47 | | ``X`` | Any type | A type to be returned. | | |
| 48 | +---------------+-------------------+-----------------------------------+ | |
| 49 | ||
| 50 | ||
| 51 | Expression semantics | |
| 52 | -------------------- | |
| 53 | ||
| 54 | For an arbitrary type ``x``: | |
| 55 | ||
| 56 | ||
| 57 | .. parsed-literal:: | |
| 58 | ||
| 59 | typedef always<x> f; | |
| 60 | ||
| 61 | :Return type: | |
| 62 | |Metafunction Class|. | |
| 63 | ||
| 64 | :Semantics: | |
| 65 | Equivalent to | |
| 66 | ||
| 67 | .. parsed-literal:: | |
| 68 | ||
| 69 | struct f : bind< identity<_1>, x > {}; | |
| 70 | ||
| 71 | ||
| 72 | Example | |
| 73 | ------- | |
| 74 | ||
| 75 | .. parsed-literal:: | |
| 76 | ||
| 77 | typedef always<true\_> always_true; | |
| 78 | ||
| 79 | BOOST_MPL_ASSERT(( apply< always_true,false\_> )); | |
| 80 | BOOST_MPL_ASSERT(( apply< always_true,false\_,false\_ > )); | |
| 81 | BOOST_MPL_ASSERT(( apply< always_true,false\_,false\_,false\_ > )); | |
| 82 | ||
| 83 | ||
| 84 | See also | |
| 85 | -------- | |
| 86 | ||
| 87 | |Metafunctions|, |Metafunction Class|, |identity|, |bind|, |apply| | |
| 88 | ||
| 89 | ||
| 90 |