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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 <ftl/details/type_traits.h>
namespace android::ftl {
template <typename>
struct Optional;
namespace details {
template <typename>
struct is_optional : std::false_type {};
template <typename T>
struct is_optional<std::optional<T>> : std::true_type {};
template <typename T>
struct is_optional<Optional<T>> : std::true_type {};
template <typename F, typename T>
struct transform_result {
using type = Optional<std::remove_cv_t<std::invoke_result_t<F, T>>>;
};
template <typename F, typename T>
using transform_result_t = typename transform_result<F, T>::type;
template <typename F, typename T>
struct and_then_result {
using type = remove_cvref_t<std::invoke_result_t<F, T>>;
static_assert(is_optional<type>{}, "and_then function must return an optional");
};
template <typename F, typename T>
using and_then_result_t = typename and_then_result<F, T>::type;
template <typename F, typename T>
struct or_else_result {
using type = remove_cvref_t<std::invoke_result_t<F>>;
static_assert(std::is_same_v<type, std::optional<T>> || std::is_same_v<type, Optional<T>>,
"or_else function must return an optional T");
};
template <typename F, typename T>
using or_else_result_t = typename or_else_result<F, T>::type;
} // namespace details
} // namespace android::ftl
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