Returning Outcome types from Coroutines

eager<T, Executor = void> and lazy<T, Executor = void> and their atomic editions are completely standard awaitables with no special behaviours, except if T is a basic_result or basic_outcome. In that situation, the following occurs:

If the Coroutine throws a C++ exception which was not handled inside the Coroutine body, Outcome’s awaitable types try to convert it into a form which your Result or Outcome type being returned can transport. For example:

• If your Coroutine were returning a result<T, std::exception_ptr>, an errored Result with a pointer to the exception thrown would be returned.

• If your Coroutine were returning a result<T, std::error_code>, the exception ptr is passed to error_from_exception( ) to see if it can be matched to an equivalent std::error_code. If it can, an errored Result with the equivalent error code would be returned.

• If your Coroutine were returning an outcome<T, std::error_code, std::exception_ptr>, an Errored Outcome is chosen preferentially to an Excepted Outcome.

• If your Coroutine were returning an experimental::status_result<T, system_code>, because Experimental SG14 system_code can transport error codes or exception ptrs (or indeed std::error_code’s), an errored Result is returned.