projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Sequences/Intrinsic Metafunctions//has_key |
| 2 | ||
| 3 | has_key | |
| 4 | ======= | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename Sequence | |
| 13 | , typename Key | |
| 14 | > | |
| 15 | struct has_key | |
| 16 | { | |
| 17 | typedef |unspecified| type; | |
| 18 | }; | |
| 19 | ||
| 20 | ||
| 21 | ||
| 22 | Description | |
| 23 | ----------- | |
| 24 | ||
| 25 | Returns a true-valued |Integral Constant| if ``Sequence`` contains an element | |
| 26 | with key ``Key``. | |
| 27 | ||
| 28 | ||
| 29 | Header | |
| 30 | ------ | |
| 31 | ||
| 32 | .. parsed-literal:: | |
| 33 | ||
| 34 | #include <boost/mpl/has_key.hpp> | |
| 35 | ||
| 36 | ||
| 37 | Model of | |
| 38 | -------- | |
| 39 | ||
| 40 | |Tag Dispatched Metafunction| | |
| 41 | ||
| 42 | ||
| 43 | Parameters | |
| 44 | ---------- | |
| 45 | ||
| 46 | +---------------+---------------------------+-----------------------------------------------+ | |
| 47 | | Parameter | Requirement | Description | | |
| 48 | +===============+===========================+===============================================+ | |
| 49 | | ``Sequence`` | |Associative Sequence| | A sequence to query. | | |
| 50 | +---------------+---------------------------+-----------------------------------------------+ | |
| 51 | | ``Key`` | Any type | The queried key. | | |
| 52 | +---------------+---------------------------+-----------------------------------------------+ | |
| 53 | ||
| 54 | ||
| 55 | Expression semantics | |
| 56 | -------------------- | |
| 57 | ||
| 58 | For any |Associative Sequence| ``s``, and arbitrary type ``key``: | |
| 59 | ||
| 60 | .. parsed-literal:: | |
| 61 | ||
| 62 | typedef has_key<s,key>::type c; | |
| 63 | ||
| 64 | :Return type: | |
| 65 | Boolean |Integral Constant|. | |
| 66 | ||
| 67 | :Semantics: | |
| 68 | ``c::value == true`` if ``key`` is in ``s``'s set of keys; otherwise | |
| 69 | ``c::value == false``. | |
| 70 | ||
| 71 | ||
| 72 | Complexity | |
| 73 | ---------- | |
| 74 | ||
| 75 | Amortized constant time. | |
| 76 | ||
| 77 | ||
| 78 | Example | |
| 79 | ------- | |
| 80 | ||
| 81 | .. parsed-literal:: | |
| 82 | ||
| 83 | typedef map< pair<int,unsigned>, pair<char,long> > m; | |
| 84 | BOOST_MPL_ASSERT_NOT(( has_key<m,long> )); | |
| 85 | ||
| 86 | typedef insert< m, pair<long,unsigned long> > m1; | |
| 87 | BOOST_MPL_ASSERT(( has_key<m1,long> )); | |
| 88 | ||
| 89 | ||
| 90 | See also | |
| 91 | -------- | |
| 92 | ||
| 93 | |Associative Sequence|, |count|, |insert|, |erase_key| | |
| 94 | ||
| 95 | ||
| 96 |