unique

Synopsis

template<
      typename Seq
    , typename Pred
    , typename In = unspecified
    >
struct unique
{
    typedef unspecified type;
};

Description

Returns a sequence of the initial elements of every subrange of the original sequence Seq whose elements are all the same.

[Note: This wording applies to a no-inserter version(s) of the algorithm. See the Expression semantics subsection for a precise specification of the algorithm's details in all cases — end note]

Header

#include <boost/mpl/unique.hpp>

Model of

Reversible Algorithm

Parameters

Parameter	Requirement	Description
`Sequence`	Forward Sequence	An original sequence.
`Pred`	Binary Lambda Expression	An equivalence relation.
`In`	Inserter	An inserter.

Expression semantics

The semantics of an expression are defined only where they differ from, or are not defined in Reversible Algorithm.

For any Forward Sequence s, a binary Lambda Expression pred, and an Inserter in:

typedef unique<s,pred,in>::type r;

Return type: A type.

Semantics:

Return type:	A type.
Semantics:	If `size<s>::value <= 1`, then equivalent to typedef copy<s,in>::type r; otherwise equivalent to typedef lambda<pred>::type p; typedef lambda<in::operation>::type in_op; typedef apply_wrap`2`< in_op , in::state , front<types>::type >::type in_state; typedef fold< s , pair< in_state, front<s>::type > , eval_if< apply_wrap`2`<p, second<_1>, _2> , identity< first<_1> > , apply_wrap`2`<in_op, first<_1>, _2> > >::type::first r;

If size<s>::value <= 1, then equivalent to

typedef copy<s,in>::type r;

otherwise equivalent to

typedef lambda<pred>::type p;
typedef lambda<in::operation>::type in_op;
typedef apply_wrap2<
      in_op
    , in::state
    , front<types>::type 
    >::type in_state;

typedef fold<
      s
    , pair< in_state, front<s>::type >
    , eval_if< 
          apply_wrap2<p, second<_1>, _2>
        , identity< first<_1> >
        , apply_wrap2<in_op, first<_1>, _2>
        >
    >::type::first r;

Complexity

Linear. Performs exactly size<s>::value - 1 applications of pred, and at most size<s>::value insertions.

Example

typedef vector<int,float,float,char,int,int,int,double> types;
typedef vector<int,float,char,int,double> expected;
typedef unique< types, is_same<_1,_2> >::type result;

BOOST_MPL_ASSERT(( equal< result,expected > ));