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116 lines
3.4 KiB
Plaintext
116 lines
3.4 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:any_range any_range]
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[heading Description]
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`any_range` is a range that has the type information erased hence a `any_range<int, boost::forward_traversal_tag, int, std::ptrdiff_t>`
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can be used to represent a `std::vector<int>`, a `std::list<int>` or many other types.
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The __type_erasure_article__ covers the motivation and goals of type erasure in this context. Clearly
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my implementation is building upon a lot of prior art created by others. Thomas Becker's `any_iterator` was a strong
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influence. Adobe also have an `any_iterator` implementation, but this has very tight coupling to other parts of the
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library that precluded it from use in Boost.Range.
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Early development versions of this Range Adaptor directly used Thomas Becker's any_iterator implementation.
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Subsequently I discovered that the heap allocations of this and many other implementations cause poor
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speed performance particularly at the tails of the distribution. To solve this required a new design that
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incorporated the embedded buffer optimization.
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Despite the underlying `any_iterator` being the fastest available implementation, the performance overhead of `any_range` is still appreciable due to the cost of virtual function calls required to implement `increment`, `decrement`, `advance`, `equal` etc. Frequently a better design choice is to convert to a canonical form.
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Please see the __range_adaptors_type_erased__ for a Range Adaptor that returns `any_range` instances.
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[heading Synopsis]
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``
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template<
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class Value
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, class Traversal
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, class Reference
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, class Difference
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, class Buffer = any_iterator_default_buffer
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>
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class any_range
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: public iterator_range<
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range_detail::any_iterator<
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Value
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, Traversal
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, Reference
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, Difference
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, Buffer
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>
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>
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{
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typedef range_detail::any_iterator<
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Value
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, Traversal
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, Reference
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, Difference
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, Buffer
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> any_iterator_type;
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typedef iterator_range<any_iterator_type> base_type;
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struct enabler {};
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struct disabler {};
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public:
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typedef any_iterator_type iterator;
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typedef any_iterator_type const_iterator;
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any_range()
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{
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}
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any_range(const any_range& other)
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: base_type(other)
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{
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}
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template<class WrappedRange>
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any_range(WrappedRange& wrapped_range)
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: base_type(boost::begin(wrapped_range),
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boost::end(wrapped_range))
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{
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}
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template<class WrappedRange>
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any_range(const WrappedRange& wrapped_range)
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: base_type(boost::begin(wrapped_range),
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boost::end(wrapped_range))
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{
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}
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template<
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class OtherValue
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, class OtherTraversal
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, class OtherReference
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, class OtherDifference
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>
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any_range(const any_range<
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OtherValue
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, OtherTraversal
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, OtherReference
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, OtherDifference
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, Buffer
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>& other)
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: base_type(boost::begin(other), boost::end(other))
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{
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}
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template<class Iterator>
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any_range(Iterator first, Iterator last)
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: base_type(first, last)
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{
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}
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};
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``
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[heading Definition]
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Defined in header file `boost/range/any_range.hpp`
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[endsect]
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