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

   1 .. Algorithms/Querying Algorithms//count_if |50
   2
   3 count_if
   4 ========
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Sequence
  13         , typename Pred
  14         >
  15     struct count_if
  16     {
  17         typedef |unspecified| type;
  18     };
  19
  20
  21
  22 Description
  23 -----------
  24
  25 Returns the number of elements in ``Sequence`` that satisfy the predicate ``Pred``.
  26
  27
  28 Header
  29 ------
  30
  31 .. parsed-literal::
  32
  33     #include <boost/mpl/count_if.hpp>
  34
  35
  36
  37 Parameters
  38 ----------
  39
  40 +---------------+-------------------------------+-----------------------------------+
  41 | Parameter     | Requirement                   | Description                       |
  42 +===============+===============================+===================================+
  43 | ``Sequence``  | |Forward Sequence|            | A sequence to be examined.        |
  44 +---------------+-------------------------------+-----------------------------------+
  45 | ``Pred``      | Unary |Lambda Expression|     | A count condition.                |
  46 +---------------+-------------------------------+-----------------------------------+
  47
  48
  49 Expression semantics
  50 --------------------
  51
  52
  53 For any |Forward Sequence| ``s`` and unary |Lambda Expression| ``pred``:
  54
  55 .. parsed-literal::
  56
  57     typedef count_if<s,pred>::type n;
  58
  59 :Return type:
  60     |Integral Constant|.
  61
  62 :Semantics:
  63     Equivalent to
  64
  65     .. parsed-literal::
  66
  67         typedef lambda<pred>::type p;
  68         typedef fold<
  69               s
  70             , long_<0>
  71             , if_< apply_wrap\ ``1``\<p,_2>, next<_1>, _1 >
  72             >::type n;
  73
  74
  75 Complexity
  76 ----------
  77
  78 Linear. Exactly ``size<s>::value`` applications of ``pred``.
  79
  80
  81 Example
  82 -------
  83
  84 .. parsed-literal::
  85
  86     typedef vector<int,char,long,short,char,long,double,long> types;
  87
  88     BOOST_MPL_ASSERT_RELATION( (count_if< types, is_float<_> >::value), ==, 1 );
  89     BOOST_MPL_ASSERT_RELATION( (count_if< types, is_same<_,char> >::value), ==, 2 );
  90     BOOST_MPL_ASSERT_RELATION( (count_if< types, is_same<_,void> >::value), ==, 0 );
  91
  92
  93 See also
  94 --------
  95
  96 |Querying Algorithms|, |count|, |find|, |find_if|, |contains|
  97
  98
  99 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 100    Distributed under the Boost Software License, Version 1.0. (See accompanying
 101    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)