- WorkEntry -> std:promise   (This class is not explicitly called. It is allocated on the heap (using new), and its ownership is passed to WorkResult.)
- WorkResult -> std: future  (With pick semantics, void type specialization, error handling, exception propagation, and optional constant reference access to the result.)
- Work                       (Contains a CoWork instance, and exposes Do() and Finish() methods.)

//	Error handling, picking/moving.
	auto r1 = work.Do([=] { throw Work::Error("Worker failed."); });
	work.Finish();
	auto r2 = pick(r1); // r1 is picked.
	if(r2.IsError()) {
		Cout() << r2.GetErrorDesc() << '\n';
	}