82 lines
1.9 KiB
C++
82 lines
1.9 KiB
C++
#pragma once
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#include <concepts>
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#include <cstddef>
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#include <ranges>
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#include <xutility>
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namespace util {
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namespace rg = std::ranges;
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namespace detail {
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template <std::invocable F> struct generated_iterator {
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using value_type = decltype(std::declval<F>()());
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using reference = value_type &;
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using difference_type = std::ptrdiff_t;
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value_type value{};
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F generator{};
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generated_iterator() = default;
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generated_iterator(const F &gen) : generator(gen), value(gen()) {}
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generated_iterator(F &&gen) : generator(std::move(gen)), value(gen()) {}
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auto generate_new_value() -> void { value = generator(); }
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constexpr auto operator==(const generated_iterator &other) const {
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return false;
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}
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auto operator++(int) -> generated_iterator {
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const auto result = *this;
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++(*this);
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return result;
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}
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auto operator++() -> generated_iterator & {
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generate_new_value();
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return (*this);
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}
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auto operator*() { return value; }
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auto operator*() const { return value; }
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};
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} // namespace detail
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template <std::invocable F>
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class generated_view : rg::view_interface<generated_view<F>> {
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F generator;
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public:
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generated_view() = default;
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constexpr generated_view(F &&generator) : generator(generator) {}
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constexpr auto begin() const { return detail::generated_iterator(generator); }
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constexpr auto end() const { return std::unreachable_sentinel; }
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};
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namespace detail {
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struct generated_range_adaptor_closure {
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template <std::invocable F> constexpr auto operator()(F &&fn) const {
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return generated_view(std::forward<F>(fn));
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}
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};
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struct generated_range_adaptor {
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template <std::invocable F> constexpr auto operator()(F &&r) {
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return generated_view(std::forward<F>(r));
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}
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constexpr auto operator()() { return generated_range_adaptor_closure(); }
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};
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} // namespace detail
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namespace views {
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inline detail::generated_range_adaptor_closure from;
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}
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} // namespace util
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