ceph/src/boost/libs/mpl/doc/src/refmanual/pop_front.rst

   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 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 109    Distributed under the Boost Software License, Version 1.0. (See accompanying
 110    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)