projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | .. Sequences/Intrinsic Metafunctions//empty |
| 2 | ||
| 3 | empty | |
| 4 | ===== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | template< | |
| 12 | typename Sequence | |
| 13 | > | |
| 14 | struct empty | |
| 15 | { | |
| 16 | typedef |unspecified| type; | |
| 17 | }; | |
| 18 | ||
| 19 | ||
| 20 | ||
| 21 | Description | |
| 22 | ----------- | |
| 23 | ||
| 24 | Returns an |Integral Constant| ``c`` such that ``c::value == true`` if | |
| 25 | and only if the sequence is empty. | |
| 26 | ||
| 27 | ||
| 28 | Header | |
| 29 | ------ | |
| 30 | ||
| 31 | .. parsed-literal:: | |
| 32 | ||
| 33 | #include <boost/mpl/empty.hpp> | |
| 34 | ||
| 35 | ||
| 36 | Model of | |
| 37 | -------- | |
| 38 | ||
| 39 | |Tag Dispatched Metafunction| | |
| 40 | ||
| 41 | ||
| 42 | Parameters | |
| 43 | ---------- | |
| 44 | ||
| 45 | +---------------+-----------------------+-----------------------------------+ | |
| 46 | | Parameter | Requirement | Description | | |
| 47 | +===============+=======================+===================================+ | |
| 48 | | ``Sequence`` | |Forward Sequence| | A sequence to test. | | |
| 49 | +---------------+-----------------------+-----------------------------------+ | |
| 50 | ||
| 51 | ||
| 52 | Expression semantics | |
| 53 | -------------------- | |
| 54 | ||
| 55 | For any |Forward Sequence| ``s``: | |
| 56 | ||
| 57 | ||
| 58 | .. parsed-literal:: | |
| 59 | ||
| 60 | typedef empty<s>::type c; | |
| 61 | ||
| 62 | :Return type: | |
| 63 | Boolean |Integral Constant|. | |
| 64 | ||
| 65 | :Semantics: | |
| 66 | Equivalent to ``typedef is_same< begin<s>::type,end<s>::type >::type c;``. | |
| 67 | ||
| 68 | :Postcondition: | |
| 69 | ``empty<s>::value == ( size<s>::value == 0 )``. | |
| 70 | ||
| 71 | ||
| 72 | ||
| 73 | Complexity | |
| 74 | ---------- | |
| 75 | ||
| 76 | Amortized constant time. | |
| 77 | ||
| 78 | ||
| 79 | Example | |
| 80 | ------- | |
| 81 | ||
| 82 | .. parsed-literal:: | |
| 83 | ||
| 84 | typedef range_c<int,0,0> empty_range; | |
| 85 | typedef vector<long,float,double> types; | |
| 86 | ||
| 87 | BOOST_MPL_ASSERT( empty<empty_range> ); | |
| 88 | BOOST_MPL_ASSERT_NOT( empty<types> ); | |
| 89 | ||
| 90 | ||
| 91 | See also | |
| 92 | -------- | |
| 93 | ||
| 94 | |Forward Sequence|, |Integral Constant|, |size|, |begin| / |end| | |
| 95 | ||
| 96 | ||
| 97 |