forked from boostorg/iterator
216 lines
7.4 KiB
C++
216 lines
7.4 KiB
C++
// (C) Copyright David Abrahams and Jeremy Siek 2000-2001. Permission to copy,
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// use, modify, sell and distribute this software is granted provided this
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// copyright notice appears in all copies. This software is provided "as is"
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// without express or implied warranty, and with no claim as to its suitability
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// for any purpose.
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//
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// See http://www.boost.org for most recent version including documentation.
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//
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// Supplies:
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//
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// template <class Incrementable> class counting_iterator_traits;
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// template <class Incrementable> class counting_iterator_policies;
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//
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// Iterator traits and policies for adapted iterators whose dereferenced
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// value progresses through consecutive values of Incrementable when the
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// iterator is derferenced.
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//
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// template <class Incrementable> struct counting_iterator_generator;
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//
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// A "type generator" whose nested type "type" is a counting iterator as
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// described above.
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//
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// template <class Incrementable>
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// typename counting_iterator_generator<Incrementable>::type
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// make_counting_iterator(Incrementable);
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//
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// A function which produces an adapted counting iterator over values of
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// Incrementable.
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//
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// Revision History
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// 14 Feb 2001 Removed unnecessary typedefs from counting_iterator_traits
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// (Jeremy Siek)
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// 11 Feb 2001 Use BOOST_STATIC_CONSTANT (Dave Abrahams)
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// 11 Feb 2001 Clean up after John Maddocks's (finally effective!) Borland
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// fixes (David Abrahams).
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// 10 Feb 2001 Use new iterator_adaptor<> interface (David Abrahams)
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// 10 Feb 2001 Rolled in supposed Borland fixes from John Maddock, but not
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// seeing any improvement yet (David Abrahams)
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// 09 Feb 2001 Factored out is_numeric computation. Borland still
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// unhappy :( (David Abrahams)
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// 08 Feb 2001 Beginning of a failed attempt to appease Borland
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// (David Abrahams)
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// 07 Feb 2001 rename counting_iterator() -> make_counting_iterator()
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// (David Abrahams)
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// 04 Feb 2001 Added counting_iterator_generator; updated comments
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// (David Abrahams)
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// 24 Jan 2001 initial revision, based on Jeremy Siek's
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// boost/pending/integer_range.hpp (David Abrahams)
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#ifndef BOOST_COUNTING_ITERATOR_HPP_DWA20000119
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# define BOOST_COUNTING_ITERATOR_HPP_DWA20000119
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# include <boost/config.hpp>
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# include <boost/detail/iterator.hpp>
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# include <boost/iterator_adaptors.hpp>
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# include <boost/type_traits.hpp>
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# include <boost/detail/numeric_traits.hpp>
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# include <boost/static_assert.hpp>
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# ifndef BOOST_NO_LIMITS
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# include <limits>
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# endif
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namespace boost {
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namespace detail {
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// Template class counting_iterator_traits_select -- choose an
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// iterator_category and difference_type for a counting_iterator at
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// compile-time based on whether or not it wraps an integer or an iterator,
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// using "poor man's partial specialization".
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template <bool is_integer> struct counting_iterator_traits_select;
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// Incrementable is an iterator type
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template <>
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struct counting_iterator_traits_select<false>
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{
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template <class Incrementable>
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struct traits
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{
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private:
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typedef boost::detail::iterator_traits<Incrementable> x;
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public:
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typedef typename x::iterator_category iterator_category;
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typedef typename x::difference_type difference_type;
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};
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};
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// Incrementable is a numeric type
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template <>
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struct counting_iterator_traits_select<true>
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{
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template <class Incrementable>
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struct traits
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{
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typedef typename
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boost::detail::numeric_traits<Incrementable>::difference_type
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difference_type;
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typedef std::random_access_iterator_tag iterator_category;
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};
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};
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// Template class distance_policy_select -- choose a policy for computing the
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// distance between counting_iterators at compile-time based on whether or not
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// the iterator wraps an integer or an iterator, using "poor man's partial
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// specialization".
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template <bool is_integer> struct distance_policy_select;
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// A policy for wrapped iterators
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template <>
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struct distance_policy_select<false>
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{
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template <class Distance, class Incrementable>
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struct policy {
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static Distance distance(Incrementable x, Incrementable y)
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{ return boost::detail::distance(x, y); }
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};
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};
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// A policy for wrapped numbers
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template <>
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struct distance_policy_select<true>
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{
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template <class Distance, class Incrementable>
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struct policy {
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static Distance distance(Incrementable x, Incrementable y)
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{ return numeric_distance(x, y); }
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};
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};
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// Try to detect numeric types at compile time in ways compatible with the
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// limitations of the compiler and library.
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template <class T>
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struct is_numeric {
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// For a while, this wasn't true, but we rely on it below. This is a regression assert.
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BOOST_STATIC_ASSERT(::boost::is_integral<char>::value);
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# ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
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BOOST_STATIC_CONSTANT(bool, value = std::numeric_limits<T>::is_specialized);
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# else
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# if !defined(__BORLANDC__)
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BOOST_STATIC_CONSTANT(bool, value = (
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boost::is_convertible<int,T>::value && boost::is_convertible<T,int>::value));
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# else
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BOOST_STATIC_CONSTANT(bool, value = ::boost::is_arithmetic<T>::value);
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# endif
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# endif
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};
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// Compute the distance over arbitrary numeric and/or iterator types
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template <class Distance, class Incrementable>
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Distance any_distance(Incrementable start, Incrementable finish, Distance* = 0)
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{
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return distance_policy_select<(
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is_numeric<Incrementable>::value)>::template
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policy<Distance, Incrementable>::distance(start, finish);
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}
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} // namespace detail
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template <class Incrementable>
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struct counting_iterator_traits {
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private:
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typedef ::boost::detail::counting_iterator_traits_select<(
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::boost::detail::is_numeric<Incrementable>::value
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)> binder;
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typedef typename binder::template traits<Incrementable> traits;
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public:
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typedef typename traits::difference_type difference_type;
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typedef typename traits::iterator_category iterator_category;
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};
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template <class Incrementable>
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struct counting_iterator_policies : public default_iterator_policies
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{
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const Incrementable& dereference(type<const Incrementable&>, const Incrementable& i) const
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{ return i; }
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template <class Difference, class Iterator1, class Iterator2>
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Difference distance(type<Difference>, const Iterator1& x,
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const Iterator2& y) const
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{
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return boost::detail::any_distance<Difference>(x, y);//,(Difference*)());
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}
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};
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// A type generator for counting iterators
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template <class Incrementable>
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struct counting_iterator_generator
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{
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typedef counting_iterator_traits<Incrementable> traits;
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typedef iterator_adaptor<Incrementable,
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counting_iterator_policies<Incrementable>,
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Incrementable,
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const Incrementable&,
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const Incrementable*,
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typename traits::iterator_category,
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typename traits::difference_type
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> type;
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};
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// Manufacture a counting iterator for an arbitrary incrementable type
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template <class Incrementable>
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inline typename counting_iterator_generator<Incrementable>::type
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make_counting_iterator(Incrementable x)
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{
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typedef typename counting_iterator_generator<Incrementable>::type result_t;
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return result_t(x);
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}
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} // namespace boost
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#endif // BOOST_COUNTING_ITERATOR_HPP_DWA20000119
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