projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Sequences/Intrinsic Metafunctions//front |
| 2 | ||
| 3 | front | |
| 4 | ===== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename Sequence | |
| 13 | > | |
| 14 | struct front | |
| 15 | { | |
| 16 | typedef |unspecified| type; | |
| 17 | }; | |
| 18 | ||
| 19 | ||
| 20 | ||
| 21 | Description | |
| 22 | ----------- | |
| 23 | ||
| 24 | Returns the first element in the sequence. | |
| 25 | ||
| 26 | ||
| 27 | Header | |
| 28 | ------ | |
| 29 | ||
| 30 | .. parsed-literal:: | |
| 31 | ||
| 32 | #include <boost/mpl/front.hpp> | |
| 33 | ||
| 34 | ||
| 35 | Model of | |
| 36 | -------- | |
| 37 | ||
| 38 | |Tag Dispatched Metafunction| | |
| 39 | ||
| 40 | ||
| 41 | Parameters | |
| 42 | ---------- | |
| 43 | ||
| 44 | +---------------+-----------------------+-----------------------------------------------+ | |
| 45 | | Parameter | Requirement | Description | | |
| 46 | +===============+=======================+===============================================+ | |
| 47 | | ``Sequence`` | |Forward Sequence| | A sequence to be examined. | | |
| 48 | +---------------+-----------------------+-----------------------------------------------+ | |
| 49 | ||
| 50 | ||
| 51 | Expression semantics | |
| 52 | -------------------- | |
| 53 | ||
| 54 | For any |Forward Sequence| ``s``: | |
| 55 | ||
| 56 | ||
| 57 | .. parsed-literal:: | |
| 58 | ||
| 59 | typedef front<s>::type t; | |
| 60 | ||
| 61 | :Return type: | |
| 62 | A type. | |
| 63 | ||
| 64 | :Precondition: | |
| 65 | ``empty<s>::value == false``. | |
| 66 | ||
| 67 | :Semantics: | |
| 68 | Equivalent to | |
| 69 | ||
| 70 | .. parsed-literal:: | |
| 71 | ||
| 72 | typedef deref< begin<s>::type >::type t; | |
| 73 | ||
| 74 | ||
| 75 | ||
| 76 | Complexity | |
| 77 | ---------- | |
| 78 | ||
| 79 | Amortized constant time. | |
| 80 | ||
| 81 | ||
| 82 | Example | |
| 83 | ------- | |
| 84 | ||
| 85 | .. parsed-literal:: | |
| 86 | ||
| 87 | typedef list<long>::type types1; | |
| 88 | typedef list<int,long>::type types2; | |
| 89 | typedef list<char,int,long>::type types3; | |
| 90 | ||
| 91 | BOOST_MPL_ASSERT(( is_same< front<types1>::type, long > )); | |
| 92 | BOOST_MPL_ASSERT(( is_same< front<types2>::type, int> )); | |
| 93 | BOOST_MPL_ASSERT(( is_same< front<types3>::type, char> )); | |
| 94 | ||
| 95 | ||
| 96 | ||
| 97 | See also | |
| 98 | -------- | |
| 99 | ||
| 100 | |Forward Sequence|, |back|, |push_front|, |begin|, |deref|, |at| | |
| 101 | ||
| 102 | ||
| 103 |