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

   1 .. Sequences/Intrinsic Metafunctions//pop_back
   2
   3 pop_back
   4 ========
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Sequence
  13         >
  14     struct pop_back
  15     {
  16         typedef |unspecified| type;
  17     };
  18
  19
  20 Description
  21 -----------
  22
  23 ``pop_back`` performs a removal at the end of the sequence with guaranteed |O(1)|
  24 complexity.
  25
  26
  27 Header
  28 ------
  29
  30 .. parsed-literal::
  31
  32     #include <boost/mpl/pop_back.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``  | |Back Extensible Sequence|    | A sequence to erase the last element from.    |
  48 +---------------+-------------------------------+-----------------------------------------------+
  49
  50
  51 Expression semantics
  52 --------------------
  53
  54 For any |Back Extensible Sequence| ``s``:
  55
  56 .. parsed-literal::
  57
  58     typedef pop_back<s>::type r;
  59
  60 :Return type:
  61     |Back Extensible Sequence|.
  62
  63 :Precondition:
  64     ``empty<s>::value == false``.
  65
  66 :Semantics:
  67     Equivalent to ``erase<s,end<s>::type>::type;``.
  68
  69 :Postcondition:
  70     ``size<r>::value == size<s>::value - 1``.
  71
  72
  73 Complexity
  74 ----------
  75
  76 Amortized constant time.
  77
  78
  79 Example
  80 -------
  81
  82 .. parsed-literal::
  83
  84     typedef vector<long>::type types1;
  85     typedef vector<long,int>::type types2;
  86     typedef vector<long,int,char>::type types3;
  87
  88     typedef pop_back<types1>::type result1;
  89     typedef pop_back<types2>::type result2;
  90     typedef pop_back<types3>::type result3;
  91
  92     BOOST_MPL_ASSERT_RELATION( size<result1>::value, ==, 0 );
  93     BOOST_MPL_ASSERT_RELATION( size<result2>::value, ==, 1 );
  94     BOOST_MPL_ASSERT_RELATION( size<result3>::value, ==, 2 );
  95
  96     BOOST_MPL_ASSERT(( is_same< back<result2>::type, long> ));
  97     BOOST_MPL_ASSERT(( is_same< back<result3>::type, int > ));
  98
  99
 100 See also
 101 --------
 102
 103 |Back Extensible Sequence|, |erase|, |push_back|, |back|, |pop_front|
 104
 105
 106 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 107    Distributed under the Boost Software License, Version 1.0. (See accompanying
 108    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)