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◆ main openmsx / src / utils / view.hh
1.4 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#ifndef VIEW_HH
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#define VIEW_HH
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#include <iterator>
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#include <ranges>
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namespace view {
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template<std::ranges::view V>
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	requires std::ranges::sized_range<V>
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class drop_back_view
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	: public std::ranges::view_interface<drop_back_view<V>>
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{
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private:
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	V base_;
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	std::size_t n_;
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public:
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	drop_back_view() = default;
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	constexpr drop_back_view(V base, std::size_t n)
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		: base_(std::move(base)), n_(n) {}
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	[[nodiscard]] constexpr V base() const& noexcept { return base_; }
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	[[nodiscard]] constexpr V base() && { return std::move(base_); }
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	[[nodiscard]] constexpr auto begin() { return std::ranges::begin(base_); }
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	[[nodiscard]] constexpr auto end() {
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		auto size = std::ranges::size(base_);
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		if (n_ >= static_cast<std::size_t>(size)) {
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			return std::ranges::begin(base_); // skip everything
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		}
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		return std::ranges::next(std::ranges::begin(base_), size - n_);
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	}
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};
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template<typename R>
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drop_back_view(R&&, std::size_t) -> drop_back_view<std::views::all_t<R>>;
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struct drop_back_fn /*: public std::ranges::range_adaptor_closure<drop_back_fn>*/
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{
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	constexpr auto operator()(std::size_t n) const {
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		return [n]<typename Range>(Range&& range) {
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			return drop_back_view{
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			        std::forward<Range>(range), n};
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		};
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	}
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	template<std::ranges::viewable_range R>
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	constexpr auto operator()(R&& r, std::size_t n) const {
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		return drop_back_view{std::forward<R>(r), n};
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	}
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};
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inline constexpr drop_back_fn drop_back;
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} // namespace view
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#endif