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1[/
2    Copyright 2010 Neil Groves
3    Distributed under the Boost Software License, Version 1.0.
4    (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
5/]
6[section:equal_range equal_range]
7
8[heading Prototype]
9
10``
11template<
12    class ForwardRange,
13    class Value
14    >
15std::pair<typename range_iterator<ForwardRange>::type,
16          typename range_iterator<ForwardRange>::type>
17equal_range(ForwardRange& rng, const Value& val);
18
19template<
20    class ForwardRange,
21    class Value
22    >
23std::pair<typename range_iterator<const ForwardRange>::type,
24          typename range_iterator<const ForwardRange>::type>
25equal_range(const ForwardRange& rng, const Value& val);
26
27template<
28    class ForwardRange,
29    class Value,
30    class SortPredicate
31    >
32std::pair<typename range_iterator<ForwardRange>::type,
33          typename range_iterator<ForwardRange>::type>
34equal_range(ForwardRange& rng, const Value& val, SortPredicate pred);
35
36template<
37    class ForwardRange,
38    class Value,
39    class SortPredicate
40    >
41std::pair<typename range_iterator<const ForwardRange>::type,
42          typename range_iterator<const ForwardRange>::type>
43equal_range(const ForwardRange& rng, const Value& val, SortPredicate pred);
44 ``
45
46[heading Description]
47
48`equal_range` returns a range in the form of a pair of iterators where all of the elements are equal to `val`. If no values are found that are equal to `val`, then an empty range is returned, hence `result.first == result.second`. For the non-predicate versions of `equal_range`  the equality of elements is determined by `operator<`.
49For the predicate versions of `equal_range` the equality of elements is determined by `pred`.
50
51[heading Definition]
52
53Defined in the header file `boost/range/algorithm/equal_range.hpp`
54
55[heading Requirements]
56
57[*For the non-predicate versions:]
58
59* `ForwardRange` is a model of the __forward_range__ Concept.
60* `Value` is a model of the `LessThanComparableConcept`.
61* The ordering of objects of type `Value` is a [*/strict weak ordering/], as defined in the `LessThanComparableConcept` requirements.
62* `ForwardRange`'s value type is the same type as `Value`.
63
64[*For the predicate versions:]
65
66* `ForwardRange` is a model of the __forward_range__ Concept.
67* `SortPredicate` is a model of the `StrictWeakOrderingConcept`.
68* `ForwardRange`'s value type is the same as `Value`.
69* `ForwardRange`'s value type is convertible to both of `SortPredicate`'s argument types.
70
71[heading Precondition:]
72
73For the non-predicate versions: `rng` is ordered in ascending order according to `operator<`.
74
75For the predicate versions: `rng` is ordered in ascending order according to `pred`.
76
77[heading Complexity]
78
79For random-access ranges, the complexity is `O(log N)`, otherwise the complexity is `O(N)`.
80
81[endsect]
82
83
84