projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Sequences/Intrinsic Metafunctions//key_type |
| 2 | ||
| 3 | key_type | |
| 4 | ======== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename Sequence | |
| 13 | , typename X | |
| 14 | > | |
| 15 | struct key_type | |
| 16 | { | |
| 17 | typedef |unspecified| type; | |
| 18 | }; | |
| 19 | ||
| 20 | ||
| 21 | ||
| 22 | Description | |
| 23 | ----------- | |
| 24 | ||
| 25 | Returns the |key| that would be used to identify ``X`` in ``Sequence``. | |
| 26 | ||
| 27 | ||
| 28 | Header | |
| 29 | ------ | |
| 30 | ||
| 31 | .. parsed-literal:: | |
| 32 | ||
| 33 | #include <boost/mpl/key_type.hpp> | |
| 34 | ||
| 35 | ||
| 36 | Model of | |
| 37 | -------- | |
| 38 | ||
| 39 | |Tag Dispatched Metafunction| | |
| 40 | ||
| 41 | ||
| 42 | Parameters | |
| 43 | ---------- | |
| 44 | ||
| 45 | +---------------+---------------------------+-----------------------------------------------+ | |
| 46 | | Parameter | Requirement | Description | | |
| 47 | +===============+===========================+===============================================+ | |
| 48 | | ``Sequence`` | |Associative Sequence| | A sequence to query. | | |
| 49 | +---------------+---------------------------+-----------------------------------------------+ | |
| 50 | | ``X`` | Any type | The type to get the |key| for. | | |
| 51 | +---------------+---------------------------+-----------------------------------------------+ | |
| 52 | ||
| 53 | ||
| 54 | Expression semantics | |
| 55 | -------------------- | |
| 56 | ||
| 57 | For any |Associative Sequence| ``s``, iterators ``pos1`` and ``pos2`` in ``s``, and an | |
| 58 | artibrary type ``x``: | |
| 59 | ||
| 60 | .. parsed-literal:: | |
| 61 | ||
| 62 | typedef key_type<s,x>::type k; | |
| 63 | ||
| 64 | :Return type: | |
| 65 | A type. | |
| 66 | ||
| 67 | :Precondition: | |
| 68 | ``x`` can be put in ``s``. | |
| 69 | ||
| 70 | :Semantics: | |
| 71 | ``k`` is the |key| that would be used to identify ``x`` in ``s``. | |
| 72 | ||
| 73 | :Postcondition: | |
| 74 | If ``key_type< s,deref<pos1>::type >::type`` is identical to | |
| 75 | ``key_type< s,deref<pos2>::type >::type`` then ``pos1`` is identical to ``pos2``. | |
| 76 | ||
| 77 | ||
| 78 | ||
| 79 | Complexity | |
| 80 | ---------- | |
| 81 | ||
| 82 | Amortized constant time. | |
| 83 | ||
| 84 | ||
| 85 | Example | |
| 86 | ------- | |
| 87 | ||
| 88 | .. parsed-literal:: | |
| 89 | ||
| 90 | typedef key_type< map<>,pair<int,unsigned> >::type k1; | |
| 91 | typedef key_type< set<>,pair<int,unsigned> >::type k2; | |
| 92 | ||
| 93 | BOOST_MPL_ASSERT(( is_same< k1,int > )); | |
| 94 | BOOST_MPL_ASSERT(( is_same< k2,pair<int,unsigned> > )); | |
| 95 | ||
| 96 | ||
| 97 | See also | |
| 98 | -------- | |
| 99 | ||
| 100 | |Associative Sequence|, |value_type|, |has_key|, |set|, |map| | |
| 101 | ||
| 102 | ||
| 103 |