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

   1 .. Sequences/Views//filter_view
   2
   3 filter_view
   4 ===========
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Sequence
  13         , typename Pred
  14         >
  15     struct filter_view
  16     {
  17         // |unspecified|
  18         // |...|
  19     };
  20
  21
  22
  23 Description
  24 -----------
  25
  26 A view into a subset of ``Sequence``\ 's elements satisfying the predicate ``Pred``.
  27
  28
  29 Header
  30 ------
  31
  32 .. parsed-literal::
  33
  34     #include <boost/mpl/filter_view.hpp>
  35
  36
  37 Model of
  38 --------
  39
  40 * |Forward Sequence|
  41
  42
  43 Parameters
  44 ----------
  45
  46 +---------------+-----------------------------------+-----------------------------------------------+
  47 | Parameter     | Requirement                       | Description                                   |
  48 +===============+===================================+===============================================+
  49 | ``Sequence``  | |Forward Sequence|                | A sequence to wrap.                           |
  50 +---------------+-----------------------------------+-----------------------------------------------+
  51 | ``Pred``      | Unary |Lambda Expression|         | A filtering predicate.                        |
  52 +---------------+-----------------------------------+-----------------------------------------------+
  53
  54
  55 Expression semantics
  56 --------------------
  57
  58 Semantics of an expression is defined only where it differs from, or is not
  59 defined in |Forward Sequence|.
  60
  61 In the following table, ``v`` is an instance of ``filter_view``, ``s`` is an arbitrary
  62 |Forward Sequence|, ``pred`` is an unary |Lambda Expression|.
  63
  64 +---------------------------------------+-----------------------------------------------------------+
  65 | Expression                            | Semantics                                                 |
  66 +=======================================+===========================================================+
  67 | .. parsed-literal::                   | A lazy |Forward Sequence| sequence of all the elements in |
  68 |                                       | the range |begin/end<s>| that satisfy the predicate       |
  69 |    filter_view<s,pred>                | ``pred``.                                                 |
  70 |    filter_view<s,pred>::type          |                                                           |
  71 +---------------------------------------+-----------------------------------------------------------+
  72 | ``size<v>::type``                     | The size of ``v``;                                        |
  73 |                                       | ``size<v>::value == count_if<s,pred>::value``;            |
  74 |                                       | linear complexity; see |Forward Sequence|.                |
  75 +---------------------------------------+-----------------------------------------------------------+
  76
  77
  78 Example
  79 -------
  80
  81 Find the largest floating type in a sequence.
  82
  83 .. parsed-literal::
  84
  85     typedef vector<int,float,long,float,char[50],long double,char> types;
  86     typedef max_element<
  87           transform_view< filter_view< types,boost::is_float<_> >, size_of<_> >
  88         >::type iter;
  89
  90     BOOST_MPL_ASSERT(( is_same< deref<iter::base>::type, long double > ));
  91
  92
  93 See also
  94 --------
  95
  96 |Sequences|, |Views|, |transform_view|, |joint_view|, |zip_view|, |iterator_range|
  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)