future.h

/*
 * Copyright (C) 2022 SKTT1Ryze. All rights reserved.
 *
 * 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 License.
 * */

#include <coroutine>
#include <functional>

template <typename T>
class Future {
 public:
  // Awaitable in C++, Future in Rust
  virtual bool await_ready();
  virtual void await_suspend(std::coroutine_handle<> h);
  virtual T await_resume();
};

template <typename T, typename U>
concept Awaitable = std::is_base_of<Future<U>, T>::value;

template <typename T, Awaitable<T> U, typename R>
class Map : Future<R> {
 public:
  U future;
  std::function<R(T)> func;

  bool await_ready() { return future.await_ready(); }
  void await_suspend(std::coroutine_handle<> h) {
    return future.await_suspend(h);
  }
  R await_resume() { return func(future.await_resume()); }

  Map(U&& future, std::function<R(T)> func) : future(future), func(func) {}
};