Case Study II: Variations of Futures

#include <coroutine>
#include <iostream>
#include <memory>
template<typename T>
struct MyFuture {
    std::shared_ptr<T> value;
    MyFuture(std::shared_ptr<T> p): value(p) {
        std::cout << "    MyFuture::MyFuture" << '\n';
    }
    ~MyFuture() { 
        std::cout << "    MyFuture::~MyFuture" << '\n';
    }
    T get() {
        std::cout << "    MyFuture::get" << '\n';
        return *value;
    }
    struct promise_type {
        std::shared_ptr<T> ptr = std::make_shared<T>();
        promise_type() {
            std::cout << "        promise_type::promise_type" << '\n';
        }
        ~promise_type() { 
            std::cout << "        promise_type::~promise_type" << '\n';
        }
        MyFuture<T> get_return_object() {
            std::cout << "        promise_type::get_return_object" << '\n';
            return ptr;
        }
        void return_value(T v) {
            std::cout << "        promise_type::return_value" << '\n';
            *ptr = v;
        }
        std::suspend_never initial_suspend() {
            std::cout << "        promise_type::initial_suspend" << '\n';
            return {};
        }
        std::suspend_never final_suspend() noexcept {
            std::cout << "        promise_type::final_suspend" << '\n';
            return {};
        }
        void unhandled_exception() {
            std::exit(1);
        }
    };
};
MyFuture<int> createFuture() {
    std::cout << "createFuture" << '\n';
    co_return 2021;
}
int main() {
    std::cout << '\n';
    auto fut = createFuture();
    auto res = fut.get();
    std::cout << "res: " << res << '\n';
    std::cout << '\n';
}