source: doc/papers/concurrency/c++-cor/fmt.cpp @ 81a05ca

#include "base.hpp"

struct fmt_cor {
        struct promise_type {
                char * _value = nullptr;

                fmt_cor get_return_object() {
                        return fmt_cor(std::experimental::coroutine_handle<promise_type>::from_promise(*this));
                }

                auto initial_suspend() { return suspend_never(); }
                auto final_suspend()   {
                        return suspend_always();
                }

                void return_void() {}

                auto yield_value(char & value) {
                        _value = &value;
                        return suspend_always();
                }

                void unhandled_exception() {}
        };

        std::experimental::coroutine_handle<promise_type> _coroutine = nullptr;

        explicit fmt_cor(std::experimental::coroutine_handle<promise_type> coroutine)
                : _coroutine(coroutine)
        {}

        ~fmt_cor() {
                if(_coroutine) { _coroutine.destroy(); }
        }

        fmt_cor() = default;
        fmt_cor(fmt_cor const &) = delete;
        fmt_cor& operator=(fmt_cor const &) = delete;

        fmt_cor(fmt_cor&& other) {
                std::swap(_coroutine, other._coroutine);
        }

        fmt_cor& operator=(fmt_cor&& other) {
                if(&other != this) {
                        _coroutine = other._coroutine;
                        other._coroutine = nullptr;
                }
                return *this;
        }

        void send(char a) {
                assert(_coroutine.promise()._value);
                *_coroutine.promise()._value = a;
                _coroutine.resume();
        }
};

fmt_cor Fmt() {
        char c;
        int g, b;
        for(;;) {
                for(g = 0; g < 5; g++) {
                        for(b = 0; b < 4; b++) {
                                co_yield c;
                                std::cout << c;
                        }
                        std::cout << "  ";
                }
                std::cout << std::endl;
        }
}

int main() {
        auto fmt = Fmt();
        for(int i = 0; i < 41; i++) {
                fmt.send('a');
        }
}