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78 lines
2.7 KiB
C++
78 lines
2.7 KiB
C++
#pragma once
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#include <type_traits>
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#include <utility>
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#include <iterator>
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/** \brief Numeric range iterator, used to represent a half-closed interval [begin, end).
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* In conjunction with std::reverse_iterator allows for forward and backward iteration
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* over corresponding interval. */
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namespace ext
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{
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/// @todo check whether difference_type should be signed (make_signed_t<T>)
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template<typename T> struct range_iterator : std::iterator<
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std::bidirectional_iterator_tag, T, T, void, T>
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{
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T current{};
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range_iterator() = default;
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range_iterator(const T t) : current(t) {}
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T operator*() const { return current; }
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range_iterator & operator++() { return ++current, *this; }
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range_iterator & operator--() { return --current, *this; }
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bool operator==(const range_iterator & other) const { return current == other.current; }
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bool operator!=(const range_iterator & other) const { return current != other.current; }
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};
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template<typename T> using reverse_range_iterator = std::reverse_iterator<range_iterator<T>>;
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/** \brief Range-based for loop adapter for (reverse_)range_iterator.
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* By and large should be in conjunction with ext::range and ext::reverse_range. */
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template<typename T, bool forward> struct range_wrapper
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{
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using value_type = typename std::remove_reference<T>::type;
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using range_iterator_t = ext::range_iterator<value_type>;
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using iterator = typename std::conditional<forward,
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range_iterator_t,
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ext::reverse_range_iterator<value_type>>::type;
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value_type begin_, end_;
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iterator begin() const { return iterator(range_iterator_t{begin_}); }
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iterator end() const { return iterator(range_iterator_t{end_}); }
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};
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/** \brief Constructs range_wrapper for forward-iteration over [begin, end) in range-based for loop.
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* Usage example:
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* for (const auto i : ext::range(0, 4)) print(i);
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* Output:
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* 0 1 2 3 */
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template<typename T1, typename T2>
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inline ext::range_wrapper<typename std::common_type<T1, T2>::type, true> range(T1 begin, T2 end)
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{
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using common_type = typename std::common_type<T1, T2>::type;
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return { static_cast<common_type>(begin), static_cast<common_type>(end) };
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}
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/** \brief Constructs range_wrapper for backward-iteration over [begin, end) in range-based for loop.
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* Usage example:
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* for (const auto i : ext::reverse_range(0, 4)) print(i);
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* Output:
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* 3 2 1 0 */
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template<typename T1, typename T2>
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inline ext::range_wrapper<typename std::common_type<T1, T2>::type, false> reverse_range(T1 begin, T2 end)
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{
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using common_type = typename std::common_type<T1, T2>::type;
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return { static_cast<common_type>(end), static_cast<common_type>(begin) };
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}
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template<typename T>
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inline ext::range_iterator<T> make_range_iterator(const T value)
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{
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return { value };
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}
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}
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