projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Algorithms/Iteration Algorithms//fold |
| 2 | ||
| 3 | fold | |
| 4 | ==== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename Sequence | |
| 13 | , typename State | |
| 14 | , typename ForwardOp | |
| 15 | > | |
| 16 | struct fold | |
| 17 | { | |
| 18 | typedef |unspecified| type; | |
| 19 | }; | |
| 20 | ||
| 21 | ||
| 22 | ||
| 23 | Description | |
| 24 | ----------- | |
| 25 | ||
| 26 | Returns the result of the successive application of binary ``ForwardOp`` to the | |
| 27 | result of the previous ``ForwardOp`` invocation (``State`` if it's the first call) | |
| 28 | and every element of the sequence in the range |begin/end<Sequence>| in order. | |
| 29 | ||
| 30 | ||
| 31 | Header | |
| 32 | ------ | |
| 33 | ||
| 34 | .. parsed-literal:: | |
| 35 | ||
| 36 | #include <boost/mpl/fold.hpp> | |
| 37 | ||
| 38 | ||
| 39 | Parameters | |
| 40 | ---------- | |
| 41 | ||
| 42 | +---------------+-------------------------------+---------------------------------------------------+ | |
| 43 | | Parameter | Requirement | Description | | |
| 44 | +===============+===============================+===================================================+ | |
| 45 | | ``Sequence`` | |Forward Sequence| | A sequence to iterate. | | |
| 46 | +---------------+-------------------------------+---------------------------------------------------+ | |
| 47 | | ``State`` | Any type | The initial state for the first ``ForwardOp`` | | |
| 48 | | | | application. | | |
| 49 | +---------------+-------------------------------+---------------------------------------------------+ | |
| 50 | | ``ForwardOp`` | Binary |Lambda Expression| | The operation to be executed on forward | | |
| 51 | | | | traversal. | | |
| 52 | +---------------+-------------------------------+---------------------------------------------------+ | |
| 53 | ||
| 54 | ||
| 55 | Expression semantics | |
| 56 | -------------------- | |
| 57 | ||
| 58 | For any |Forward Sequence| ``s``, binary |Lambda Expression| ``op``, and arbitrary type ``state``: | |
| 59 | ||
| 60 | ||
| 61 | .. parsed-literal:: | |
| 62 | ||
| 63 | typedef fold<s,state,op>::type t; | |
| 64 | ||
| 65 | :Return type: | |
| 66 | A type. | |
| 67 | ||
| 68 | :Semantics: | |
| 69 | Equivalent to | |
| 70 | ||
| 71 | .. parsed-literal:: | |
| 72 | ||
| 73 | typedef iter_fold< | |
| 74 | s | |
| 75 | , state | |
| 76 | , apply_wrap2< lambda<op>::type, _1, deref<_2> > | |
| 77 | >::type t; | |
| 78 | ||
| 79 | ||
| 80 | Complexity | |
| 81 | ---------- | |
| 82 | ||
| 83 | Linear. Exactly ``size<s>::value`` applications of ``op``. | |
| 84 | ||
| 85 | ||
| 86 | Example | |
| 87 | ------- | |
| 88 | ||
| 89 | .. parsed-literal:: | |
| 90 | ||
| 91 | typedef vector<long,float,short,double,float,long,long double> types; | |
| 92 | typedef fold< | |
| 93 | types | |
| 94 | , int_<0> | |
| 95 | , if_< is_float<_2>,next<_1>,_1 > | |
| 96 | >::type number_of_floats; | |
| 97 | ||
| 98 | BOOST_MPL_ASSERT_RELATION( number_of_floats::value, ==, 4 ); | |
| 99 | ||
| 100 | ||
| 101 | See also | |
| 102 | -------- | |
| 103 | ||
| 104 | |Algorithms|, |accumulate|, |reverse_fold|, |iter_fold|, |reverse_iter_fold|, |copy|, |copy_if| | |
| 105 | ||
| 106 | ||
| 107 |