projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Sequences/Intrinsic Metafunctions//size |
| 2 | ||
| 3 | size | |
| 4 | ==== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename Sequence | |
| 13 | > | |
| 14 | struct size | |
| 15 | { | |
| 16 | typedef |unspecified| type; | |
| 17 | }; | |
| 18 | ||
| 19 | ||
| 20 | ||
| 21 | Description | |
| 22 | ----------- | |
| 23 | ||
| 24 | ``size`` returns the number of elements in the sequence, that is, the number of elements | |
| 25 | in the range [``begin<Sequence>::type``, ``end<Sequence>::type``). | |
| 26 | ||
| 27 | ||
| 28 | Header | |
| 29 | ------ | |
| 30 | ||
| 31 | .. parsed-literal:: | |
| 32 | ||
| 33 | #include <boost/mpl/size.hpp> | |
| 34 | ||
| 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`` | |Forward Sequence| | A sequence to query. | | |
| 50 | +---------------+-----------------------+-----------------------------------------------+ | |
| 51 | ||
| 52 | ||
| 53 | Expression semantics | |
| 54 | -------------------- | |
| 55 | ||
| 56 | ||
| 57 | For any |Forward Sequence| ``s``: | |
| 58 | ||
| 59 | ||
| 60 | .. parsed-literal:: | |
| 61 | ||
| 62 | typedef size<s>::type n; | |
| 63 | ||
| 64 | :Return type: | |
| 65 | |Integral Constant|. | |
| 66 | ||
| 67 | :Semantics: | |
| 68 | Equivalent to | |
| 69 | ||
| 70 | .. parsed-literal:: | |
| 71 | ||
| 72 | typedef distance< begin<s>::type,end<s>::type >::type n; | |
| 73 | ||
| 74 | ||
| 75 | :Postcondition: | |
| 76 | ``n::value >= 0``. | |
| 77 | ||
| 78 | ||
| 79 | ||
| 80 | Complexity | |
| 81 | ---------- | |
| 82 | ||
| 83 | The complexity of the ``size`` metafunction directly depends on the implementation of | |
| 84 | the particular sequence it is applied to. In the worst case, ``size`` guarantees a | |
| 85 | linear complexity. | |
| 86 | ||
| 87 | If the ``s`` is a |Random Access Sequence|, ``size<s>::type`` is an |O(1)| operation. | |
| 88 | The opposite is not necessarily true |--| for example, a sequence class that models | |
| 89 | |Forward Sequence| might still give us an |O(1)| ``size`` implementation. | |
| 90 | ||
| 91 | ||
| 92 | Example | |
| 93 | ------- | |
| 94 | ||
| 95 | .. parsed-literal:: | |
| 96 | ||
| 97 | typedef list0<> empty_list; | |
| 98 | typedef vector_c<int,0,1,2,3,4,5> numbers; | |
| 99 | typedef range_c<int,0,100> more_numbers; | |
| 100 | ||
| 101 | BOOST_MPL_ASSERT_RELATION( size<list>::value, ==, 0 ); | |
| 102 | BOOST_MPL_ASSERT_RELATION( size<numbers>::value, ==, 5 ); | |
| 103 | BOOST_MPL_ASSERT_RELATION( size<more_numbers>::value, ==, 100 ); | |
| 104 | ||
| 105 | ||
| 106 | See also | |
| 107 | -------- | |
| 108 | ||
| 109 | |Forward Sequence|, |Random Access Sequence|, |empty|, |begin|, |end|, |distance| | |
| 110 | ||
| 111 | ||
| 112 |