simple_generator.h

#ifndef EXPERIMENTAL_SIMPLE_GENERATOR
# define EXPERIMENTAL_SIMPLE_GENERATOR
#include <experimental/coroutine>

namespace std::experimental {
template <typename T> struct generator {
  struct promise_type {
    T current_value;
    suspend_always yield_value(T value) {
      this->current_value = value;
      return {};
    }
    suspend_always initial_suspend() { return {}; }
    suspend_always final_suspend() { return {}; }
    generator get_return_object() { return generator{this}; };
    void unhandled_exception() { std::terminate(); }
    void return_void() {}
  };

  struct iterator {
    coroutine_handle<promise_type> _Coro;
    bool _Done;

    iterator(coroutine_handle<promise_type> Coro, bool Done)
        : _Coro(Coro), _Done(Done) {}

    iterator &operator++() {
      _Coro.resume();
      _Done = _Coro.done();
      return *this;
    }

    bool operator==(iterator const &_Right) const {
      return _Done == _Right._Done;
    }

    bool operator!=(iterator const &_Right) const { return !(*this == _Right); }
    T const &operator*() const { return _Coro.promise().current_value; }
    T const *operator->() const { return &(operator*()); }
  };

  iterator begin() {
    p.resume();
    return {p, p.done()};
  }

  iterator end() { return {p, true}; }

  generator(generator const&) = delete;
  generator(generator &&rhs) : p(rhs.p) { rhs.p = nullptr; }

  ~generator() {
    if (p)
      p.destroy();
  }

private:
  explicit generator(promise_type *p)
      : p(coroutine_handle<promise_type>::from_promise(*p)) {}

  coroutine_handle<promise_type> p;
};
}
#endif