C++ 20 New Features

---

Coroutines

The "coroutine" concept is a function but unlike a normal function it does not terminate upon return but can suspend it's state and resume the execution later on. We also need to set up code for a coroutine that consists of a class that contains an inner class called a "promise_type" . This dictates the internal behavior of the coroutine.

File: co1.cpp

std::suspend_always
  await_ready() true -- do not suspend
                false suspends --

  await_suspend() Does nothing
  await_resume()  Does nothing

std::suspend_never
  await_ready()
  await_suspend()
  await_resume()


If a function contains the words "co_await" , co_yield" or "co_await"
then that function is a coroutine. However we need to define certain classes
such as "promise_type" in order to get the framework working.

To specify that the 20 version compiler should be used we need
to run the statement:

$ g++ -std=c++20 co1.cpp ; ./a.exe



struct SimpleCoroutine
{
    struct promise_type
    {
        SimpleCoroutine get_return_object()
        {
			cout << "get_return_object()" << endl ;
			return {};
		}
        std::suspend_never initial_suspend()
        {
			cout << "initial_suspend()" << endl ;
			return {};
		}
        std::suspend_never final_suspend() noexcept
        {
			cout << "suspend_never final_suspend()" << endl ;
			return {};
        }
        void return_void()
        {
			cout << "return_void()" << endl ;
		}
        void unhandled_exception()
        {
			cout << "unhandled_exception()" << endl ;
		}
    };
};