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◆ main openmsx / src / utils / enumerate.hh
1.4 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
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#ifndef ENUMERATE_HH
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#define ENUMERATE_HH
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/** Heavily inspired by Nathan Reed's blog post:
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  * Python-Like enumerate() In C++17
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  * http://reedbeta.com/blog/python-like-enumerate-in-cpp17/
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  *
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  * Can be used to simplify loops like:
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  *    for (size_t i = 0; i < std::size(my_array); ++i) {
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  *        auto& elem = my_array[i];
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  *        ... do stuff with 'i' and 'elem'
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  *    }
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  *
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  * With enumerate() that becomes:
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  *    for (auto [i, elem] : enumerate(my_array)) {
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  *        ... do stuff with 'i' and 'elem'
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  *    }
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  */
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#include <cstddef>
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#include <iterator>
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#include <tuple>
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#include <utility>
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template<typename Iterable,
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         typename Iter = decltype(std::begin(std::declval<Iterable>())),
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         typename      = decltype(std::end  (std::declval<Iterable>()))>
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constexpr auto enumerate(Iterable&& iterable)
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{
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	struct iterator {
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		size_t i;
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		Iter iter;
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		[[nodiscard]] constexpr bool operator==(const iterator& other) const {
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			return iter == other.iter;
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		}
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		[[nodiscard]] constexpr bool operator==(const Iter& other) const {
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			return iter == other;
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		}
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		constexpr void operator++() {
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			++i;
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			++iter;
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		}
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		constexpr auto operator*() const {
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			return std::tie(i, *iter);
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		}
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	};
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	struct iterable_wrapper {
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		Iterable iterable;
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		constexpr auto begin() {
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			return iterator{0, std::begin(iterable)};
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		}
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		constexpr auto end() {
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			return std::end(iterable);
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		}
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	};
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	return iterable_wrapper{std::forward<Iterable>(iterable)};
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}
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#endif