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/*
* Copyright 2022 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <functional>
#include <optional>
#include <type_traits>
#include <utility>
namespace android::ftl {
// Superset of std::optional<T> with monadic operations, as proposed in https://wg21.link/P0798R8.
//
// TODO: Remove in C++23.
//
template <typename T>
struct Optional final : std::optional<T> {
using std::optional<T>::optional;
using std::optional<T>::has_value;
using std::optional<T>::value;
// Returns Optional<U> where F is a function that maps T to U.
template <typename F>
constexpr auto transform(F&& f) const& {
using U = std::remove_cv_t<std::invoke_result_t<F, decltype(value())>>;
if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), value()));
return Optional<U>();
}
template <typename F>
constexpr auto transform(F&& f) & {
using U = std::remove_cv_t<std::invoke_result_t<F, decltype(value())>>;
if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), value()));
return Optional<U>();
}
template <typename F>
constexpr auto transform(F&& f) const&& {
using U = std::invoke_result_t<F, decltype(std::move(value()))>;
if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), std::move(value())));
return Optional<U>();
}
template <typename F>
constexpr auto transform(F&& f) && {
using U = std::invoke_result_t<F, decltype(std::move(value()))>;
if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), std::move(value())));
return Optional<U>();
}
};
// Deduction guide.
template <typename T>
Optional(T) -> Optional<T>;
} // namespace android::ftl
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