projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Algorithms/Querying Algorithms//count_if |50 |
| 2 | ||
| 3 | count_if | |
| 4 | ======== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename Sequence | |
| 13 | , typename Pred | |
| 14 | > | |
| 15 | struct count_if | |
| 16 | { | |
| 17 | typedef |unspecified| type; | |
| 18 | }; | |
| 19 | ||
| 20 | ||
| 21 | ||
| 22 | Description | |
| 23 | ----------- | |
| 24 | ||
| 25 | Returns the number of elements in ``Sequence`` that satisfy the predicate ``Pred``. | |
| 26 | ||
| 27 | ||
| 28 | Header | |
| 29 | ------ | |
| 30 | ||
| 31 | .. parsed-literal:: | |
| 32 | ||
| 33 | #include <boost/mpl/count_if.hpp> | |
| 34 | ||
| 35 | ||
| 36 | ||
| 37 | Parameters | |
| 38 | ---------- | |
| 39 | ||
| 40 | +---------------+-------------------------------+-----------------------------------+ | |
| 41 | | Parameter | Requirement | Description | | |
| 42 | +===============+===============================+===================================+ | |
| 43 | | ``Sequence`` | |Forward Sequence| | A sequence to be examined. | | |
| 44 | +---------------+-------------------------------+-----------------------------------+ | |
| 45 | | ``Pred`` | Unary |Lambda Expression| | A count condition. | | |
| 46 | +---------------+-------------------------------+-----------------------------------+ | |
| 47 | ||
| 48 | ||
| 49 | Expression semantics | |
| 50 | -------------------- | |
| 51 | ||
| 52 | ||
| 53 | For any |Forward Sequence| ``s`` and unary |Lambda Expression| ``pred``: | |
| 54 | ||
| 55 | .. parsed-literal:: | |
| 56 | ||
| 57 | typedef count_if<s,pred>::type n; | |
| 58 | ||
| 59 | :Return type: | |
| 60 | |Integral Constant|. | |
| 61 | ||
| 62 | :Semantics: | |
| 63 | Equivalent to | |
| 64 | ||
| 65 | .. parsed-literal:: | |
| 66 | ||
| 67 | typedef lambda<pred>::type p; | |
| 68 | typedef fold< | |
| 69 | s | |
| 70 | , long_<0> | |
| 71 | , if_< apply_wrap\ ``1``\<p,_2>, next<_1>, _1 > | |
| 72 | >::type n; | |
| 73 | ||
| 74 | ||
| 75 | Complexity | |
| 76 | ---------- | |
| 77 | ||
| 78 | Linear. Exactly ``size<s>::value`` applications of ``pred``. | |
| 79 | ||
| 80 | ||
| 81 | Example | |
| 82 | ------- | |
| 83 | ||
| 84 | .. parsed-literal:: | |
| 85 | ||
| 86 | typedef vector<int,char,long,short,char,long,double,long> types; | |
| 87 | ||
| 88 | BOOST_MPL_ASSERT_RELATION( (count_if< types, is_float<_> >::value), ==, 1 ); | |
| 89 | BOOST_MPL_ASSERT_RELATION( (count_if< types, is_same<_,char> >::value), ==, 2 ); | |
| 90 | BOOST_MPL_ASSERT_RELATION( (count_if< types, is_same<_,void> >::value), ==, 0 ); | |
| 91 | ||
| 92 | ||
| 93 | See also | |
| 94 | -------- | |
| 95 | ||
| 96 | |Querying Algorithms|, |count|, |find|, |find_if|, |contains| | |
| 97 | ||
| 98 | ||
| 99 |