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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
namespace android::ftl {
template <typename, template <typename> class>
class Future;
namespace details {
template <typename T>
struct future_result {
using type = T;
};
template <typename T>
struct future_result<std::future<T>> {
using type = T;
};
template <typename T>
struct future_result<std::shared_future<T>> {
using type = T;
};
template <typename T, template <typename> class FutureImpl>
struct future_result<Future<T, FutureImpl>> {
using type = T;
};
template <typename T>
using future_result_t = typename future_result<T>::type;
struct ValueTag {};
template <typename, typename T, template <typename> class>
class BaseFuture;
template <typename Self, typename T>
class BaseFuture<Self, T, std::future> {
using Impl = std::future<T>;
public:
Future<T, std::shared_future> share() {
if (T* value = std::get_if<T>(&self())) {
return {ValueTag{}, std::move(*value)};
}
return std::get<Impl>(self()).share();
}
protected:
T get() {
if (T* value = std::get_if<T>(&self())) {
return std::move(*value);
}
return std::get<Impl>(self()).get();
}
template <class Rep, class Period>
std::future_status wait_for(const std::chrono::duration<Rep, Period>& timeout_duration) const {
if (std::holds_alternative<T>(self())) {
return std::future_status::ready;
}
return std::get<Impl>(self()).wait_for(timeout_duration);
}
private:
auto& self() { return static_cast<Self&>(*this).future_; }
const auto& self() const { return static_cast<const Self&>(*this).future_; }
};
template <typename Self, typename T>
class BaseFuture<Self, T, std::shared_future> {
using Impl = std::shared_future<T>;
protected:
const T& get() const {
if (const T* value = std::get_if<T>(&self())) {
return *value;
}
return std::get<Impl>(self()).get();
}
template <class Rep, class Period>
std::future_status wait_for(const std::chrono::duration<Rep, Period>& timeout_duration) const {
if (std::holds_alternative<T>(self())) {
return std::future_status::ready;
}
return std::get<Impl>(self()).wait_for(timeout_duration);
}
private:
const auto& self() const { return static_cast<const Self&>(*this).future_; }
};
} // namespace details
} // namespace android::ftl
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