boost/libs/mpl/doc/src/refmanual/unique.rst

   1 .. Algorithms/Transformation Algorithms//unique |80
   2
   3 unique
   4 ======
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Seq
  13         , typename Pred
  14         , typename In = |unspecified|
  15         >
  16     struct unique
  17     {
  18         typedef |unspecified| type;
  19     };
  20
  21
  22 Description
  23 -----------
  24
  25 Returns a sequence of the initial elements of every subrange of the
  26 original sequence ``Seq`` whose elements are all the same.
  27
  28 |transformation algorithm disclaimer|
  29
  30 Header
  31 ------
  32
  33 .. parsed-literal::
  34
  35     #include <boost/mpl/unique.hpp>
  36
  37
  38 Model of
  39 --------
  40
  41 |Reversible Algorithm|
  42
  43
  44 Parameters
  45 ----------
  46
  47 +---------------+-----------------------------------+-------------------------------+
  48 | Parameter     | Requirement                       | Description                   |
  49 +===============+===================================+===============================+
  50 | ``Sequence``  | |Forward Sequence|                | An original sequence.         |
  51 +---------------+-----------------------------------+-------------------------------+
  52 | ``Pred``      | Binary |Lambda Expression|        | An equivalence relation.      |
  53 +---------------+-----------------------------------+-------------------------------+
  54 | ``In``        | |Inserter|                        | An inserter.                  |
  55 +---------------+-----------------------------------+-------------------------------+
  56
  57
  58 Expression semantics
  59 --------------------
  60
  61 |Semantics disclaimer...| |Reversible Algorithm|.
  62
  63 For any |Forward Sequence| ``s``, a binary |Lambda Expression| ``pred``,
  64 and an |Inserter| ``in``:
  65
  66
  67 .. parsed-literal::
  68
  69     typedef unique<s,pred,in>::type r;
  70
  71 :Return type:
  72     A type.
  73
  74 :Semantics:
  75     If ``size<s>::value <= 1``, then equivalent to
  76
  77     .. parsed-literal::
  78
  79         typedef copy<s,in>::type r;
  80
  81     otherwise equivalent to
  82
  83     .. parsed-literal::
  84
  85         typedef lambda<pred>::type p;
  86         typedef lambda<in::operation>::type in_op;
  87         typedef apply_wrap\ ``2``\<
  88               in_op
  89             , in::state
  90             , front<types>::type
  91             >::type in_state;
  92
  93         typedef fold<
  94               s
  95             , pair< in_state, front<s>::type >
  96             , eval_if<
  97                   apply_wrap\ ``2``\<p, second<_1>, _2>
  98                 , identity< first<_1> >
  99                 , apply_wrap\ ``2``\<in_op, first<_1>, _2>
 100                 >
 101             >::type::first r;
 102
 103
 104 Complexity
 105 ----------
 106
 107 Linear. Performs exactly ``size<s>::value - 1`` applications of ``pred``, and at
 108 most ``size<s>::value`` insertions.
 109
 110
 111 Example
 112 -------
 113
 114 .. parsed-literal::
 115
 116     typedef vector<int,float,float,char,int,int,int,double> types;
 117     typedef vector<int,float,char,int,double> expected;
 118     typedef unique< types, is_same<_1,_2> >::type result;
 119
 120     BOOST_MPL_ASSERT(( equal< result,expected > ));
 121
 122
 123 See also
 124 --------
 125
 126 |Transformation Algorithms|, |Reversible Algorithm|, |reverse_unique|, |remove|, |copy_if|, |replace_if|