87 lines
2.2 KiB
C++
87 lines
2.2 KiB
C++
#pragma once
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#include <stdx/compiler.hpp>
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#include <stdx/functional.hpp>
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#include <stdx/type_traits.hpp>
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#include <optional>
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#include <type_traits>
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#include <utility>
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namespace stdx {
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inline namespace v1 {
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template <typename F> struct cached {
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using value_type = stdx::remove_cvref_t<std::invoke_result_t<F>>;
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constexpr explicit cached(F const &f) : lazy{f} {}
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constexpr explicit cached(F &&f) : lazy{std::move(f)} {}
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constexpr auto has_value() const noexcept -> bool {
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return opt.has_value();
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}
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constexpr explicit operator bool() const noexcept {
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return opt.has_value();
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}
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constexpr auto value() & LIFETIMEBOUND -> value_type & {
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populate();
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return *opt;
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}
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constexpr auto value() const & LIFETIMEBOUND -> value_type const & {
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populate();
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return *opt;
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}
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constexpr auto value() && LIFETIMEBOUND -> value_type && {
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populate();
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return *std::move(opt);
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}
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constexpr auto value() const && LIFETIMEBOUND -> value_type const && {
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populate();
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return *std::move(opt);
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}
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constexpr auto operator->() const LIFETIMEBOUND->value_type const * {
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populate();
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return opt.operator->();
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}
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constexpr auto operator->() LIFETIMEBOUND->value_type * {
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populate();
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return opt.operator->();
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}
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constexpr auto operator*() const & LIFETIMEBOUND->decltype(auto) {
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return value();
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}
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constexpr auto operator*() & LIFETIMEBOUND->decltype(auto) {
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return value();
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}
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constexpr auto operator*() const && LIFETIMEBOUND->decltype(auto) {
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return std::move(*this).value();
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}
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constexpr auto operator*() && LIFETIMEBOUND->decltype(auto) {
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return std::move(*this).value();
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}
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auto reset() { opt.reset(); }
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auto refresh() LIFETIMEBOUND -> value_type & {
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opt.reset();
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populate();
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return *opt;
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}
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private:
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constexpr auto populate() const {
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if (not opt.has_value()) {
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opt.emplace(lazy);
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}
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}
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with_result_of<F> lazy;
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mutable std::optional<value_type> opt{};
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};
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template <typename C>
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using cached_value_t = typename stdx::remove_cvref_t<C>::value_type;
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} // namespace v1
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} // namespace stdx
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