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85 lines
2.4 KiB
Plaintext
85 lines
2.4 KiB
Plaintext
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Copyright 2010 Neil Groves
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section:indexed indexed]
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[table
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[[Syntax] [Code]]
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[[Pipe] [`rng | boost::adaptors::indexed()`]]
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[[Pipe] [`rng | boost::adaptors::indexed(start_index)`]]
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[[Function] [`boost::adaptors::index(rng)`]]
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[[Function] [`boost::adaptors::index(rng, start_index)`]]
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]
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[heading Description]
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The index within each returned `boost::range::index_value` is equal to
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`start_index` + the offset of the element from the beginning of the range. In
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the versions of the functions that omit `start_index` the starting index is
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taken to be `0`.
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* [*Purpose:] Adapt `rng` to return elements that have the corresponding value
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from `rng` and a numeric index.
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* [*Returns:] A range adapted to return both the element and the associated
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index. The returned range has elements of type:
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``
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boost::range::index_value<
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typename boost::range_reference<decltype(rng)>::type,
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typename boost::range_difference<decltype(rng)>::type
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>
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``
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The synopsis of index_value is as follows:
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``
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template<class T, class Indexable=std::ptrdiff_t>
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class index_value : public boost::tuple<Indexable, T>
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{
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public:
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typedef ...unspecified... index_type;
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typedef ...unspecified... const_index_type;
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typedef ...unspecified... value_type;
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typedef ...unspecified... const_value_type;
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// ...unspecified... constructors
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index_type index();
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const_index_type index() const;
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value_type value();
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const_value_type value() const;
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};
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``
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* [*Range Category:] __single_pass_range__
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* [*Range Return Type:] `boost::indexed_range<decltype(rng)>`
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* [*Returned Range Category:] The range category of `rng` if and only if `rng`
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is not a __bidirectional_range__. If `rng` is a __bidirectional_range__ then the
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returned range category is __forward_range__. The rationale for the demotion of
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__bidirectional_range__ inputs to __forward_range__ is to avoid slow calculation
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of indices for `boost::end(rng)`.
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[section:indexed_example indexed example]
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[import ../../../test/adaptor_test/indexed_example.cpp]
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[indexed_example]
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[endsect]
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This would produce the output:
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``
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Element = 10 Index = 0
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Element = 20 Index = 1
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Element = 30 Index = 2
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Element = 40 Index = 3
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Element = 50 Index = 4
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Element = 60 Index = 5
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Element = 70 Index = 6
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Element = 80 Index = 7
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Element = 90 Index = 8
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``
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[endsect]
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