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any_range
is a range that
has the type information erased hence a any_range<int, boost::forward_pass_traversal_tag, int,
std::ptrdiff_t>
can be used to represent a std::vector<int>
, a std::list<int>
or many other types.
The type
erasure article covers the motivation and goals of type erasure
in this context. Clearly my implementation is building upon a lot of prior
art created by others. Thomas Becker's any_iterator
was a strong influence. Adobe also have an any_iterator
implementation, but this has very tight coupling to other parts of the
library that precluded it from use in Boost.Range. Early development versions
of this Range Adaptor directly used Thomas Becker's any_iterator implementation.
Subsequently I discovered that the heap allocations of this and many other
implementations cause poor speed performance particularly at the tails
of the distribution. To solve this required a new design that incorporated
the embedded buffer optimization.
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.
Please see the type_erased
for a Range Adaptor that returns any_range
instances.
template< class Value , class Traversal , class Reference , class Difference , class Buffer = any_iterator_default_buffer > class any_range : public iterator_range< range_detail::any_iterator< Value , Traversal , Reference , Difference , Buffer > > { typedef range_detail::any_iterator< Value , Traversal , Reference , Difference , Buffer > any_iterator_type; typedef iterator_range<any_iterator_type> base_type; struct enabler {}; struct disabler {}; public: typedef any_iterator_type iterator; typedef any_iterator_type const_iterator; any_range() { } any_range(const any_range& other) : base_type(other) { } template<class WrappedRange> any_range(WrappedRange& wrapped_range) : base_type(boost::begin(wrapped_range), boost::end(wrapped_range)) { } template<class WrappedRange> any_range(const WrappedRange& wrapped_range) : base_type(boost::begin(wrapped_range), boost::end(wrapped_range)) { } template< class OtherValue , class OtherTraversal , class OtherReference , class OtherDifference > any_range(const any_range< OtherValue , OtherTraversal , OtherReference , OtherDifference , Buffer >& other) : base_type(boost::begin(other), boost::end(other)) { } template<class Iterator> any_range(Iterator first, Iterator last) : base_type(first, last) { } };
Defined in header file boost/range/any_range.hpp