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1 | .. Sequences/Intrinsic Metafunctions//pop_front |
2 | ||
3 | pop_front | |
4 | ========= | |
5 | ||
6 | Synopsis | |
7 | -------- | |
8 | ||
9 | .. parsed-literal:: | |
10 | ||
11 | template< | |
12 | typename Sequence | |
13 | > | |
14 | struct pop_front | |
15 | { | |
16 | typedef |unspecified| type; | |
17 | }; | |
18 | ||
19 | ||
20 | ||
21 | Description | |
22 | ----------- | |
23 | ||
24 | ``pop_front`` performs a removal at the beginning of the sequence with guaranteed |O(1)| | |
25 | complexity. | |
26 | ||
27 | ||
28 | Header | |
29 | ------ | |
30 | ||
31 | .. parsed-literal:: | |
32 | ||
33 | #include <boost/mpl/pop_front.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`` | |Front Extensible Sequence| | A sequence to erase the first element from. | | |
50 | +---------------+-----------------------------------+-----------------------------------------------+ | |
51 | ||
52 | ||
53 | Expression semantics | |
54 | -------------------- | |
55 | ||
56 | For any |Front Extensible Sequence| ``s``: | |
57 | ||
58 | .. parsed-literal:: | |
59 | ||
60 | typedef pop_front<s>::type r; | |
61 | ||
62 | :Return type: | |
63 | |Front Extensible Sequence|. | |
64 | ||
65 | :Precondition: | |
66 | ``empty<s>::value == false``. | |
67 | ||
68 | :Semantics: | |
69 | Equivalent to ``erase<s,begin<s>::type>::type;``. | |
70 | ||
71 | :Postcondition: | |
72 | ``size<r>::value == size<s>::value - 1``. | |
73 | ||
74 | ||
75 | Complexity | |
76 | ---------- | |
77 | ||
78 | Amortized constant time. | |
79 | ||
80 | ||
81 | Example | |
82 | ------- | |
83 | ||
84 | .. parsed-literal:: | |
85 | ||
86 | typedef vector<long>::type types1; | |
87 | typedef vector<int,long>::type types2; | |
88 | typedef vector<char,int,long>::type types3; | |
89 | ||
90 | typedef pop_front<types1>::type result1; | |
91 | typedef pop_front<types2>::type result2; | |
92 | typedef pop_front<types3>::type result3; | |
93 | ||
94 | BOOST_MPL_ASSERT_RELATION( size<result1>::value, ==, 0 ); | |
95 | BOOST_MPL_ASSERT_RELATION( size<result2>::value, ==, 1 ); | |
96 | BOOST_MPL_ASSERT_RELATION( size<result3>::value, ==, 2 ); | |
97 | ||
98 | BOOST_MPL_ASSERT(( is_same< front<result2>::type, long > )); | |
99 | BOOST_MPL_ASSERT(( is_same< front<result3>::type, int > )); | |
100 | ||
101 | ||
102 | See also | |
103 | -------- | |
104 | ||
105 | |Front Extensible Sequence|, |erase|, |push_front|, |front|, |pop_back| | |
106 | ||
107 | ||
108 |