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##### unique

###### Prototype

    template<class ForwardRange>
    typename range_return<ForwardRange, return_begin_found>::type
    unique(ForwardRange& rng);

    template<class ForwardRange>
    typename range_return<const ForwardRange, return_begin_found>::type
    unique(const ForwardRange& rng);

    template<class ForwardRange, class BinaryPredicate>
    typename range_return<ForwardRange, return_begin_found>::type
    unique(ForwardRange& rng, BinaryPredicate pred);

    template<class ForwardRange, class BinaryPredicate>
    typename range_return<const ForwardRange, return_begin_found>::type
    unique(const ForwardRange& rng, BinaryPredicate pred);

    template<range_return_value re, class ForwardRange>
    typename range_return<ForwardRange, re>::type
    unique(ForwardRange& rng);

    template<range_return_value re, class ForwardRange>
    typename range_return<const ForwardRange, re>::type
    unique(const ForwardRange& rng);

    template<range_return_value re, class ForwardRange, class BinaryPredicate>
    typename range_return<ForwardRange, re>::type
    unique(ForwardRange& rng, BinaryPredicate pred);

    template<range_return_value re, class ForwardRange, class BinaryPredicate>
    typename range_return<const ForwardRange, re>::type
    unique(const ForwardRange& rng, BinaryPredicate pred);

###### Description

`unique` removes all but the first element of each sequence of duplicate encountered in `rng`.

Elements in the range `[new_last, end(rng))` are dereferenceable but undefined.

Equality is determined by the predicate if one is supplied, or by `operator==()` for `ForwardRange`'s value type.

###### Definition

Defined in the header file `boost/range/algorithm/unique.hpp`

###### Requirements

For the non-predicate versions of unique:

- `ForwardRange` is a model of the Forward Range Concept.
- `ForwardRange` is mutable.
- `ForwardRange`'s value type is a model of the `EqualityComparableConcept`.

For the predicate versions of unique:

- `ForwardRange` is a model of the Forward Range Concept.
- `ForwardRange` is mutable.
- `BinaryPredicate` is a model of the `BinaryPredicateConcept`.
- `ForwardRange`'s value type is convertible to `BinaryPredicate`'s first argument type and to `BinaryPredicate`'s second argument type.

###### Complexity

Linear. `O(N)` where `N` is `distance(rng)`. Exactly `distance(rng)` comparisons are performed.