If my interface must return Task what is the best way to have a no-operation implementation?

Question

In the code below, due to the interface, the class LazyBar must return a task from its method (and for argument\'s sake can\'t be changed). If LazyBar

Answer 1

Task.Delay(0) as in the accepted answer was a good approach, as it is a cached copy of a completed Task.

As of 4.6 there's now Task.CompletedTask which is more explicit in its purpose, but not only does Task.Delay(0) still return a single cached instance, it returns the same single cached instance as does Task.CompletedTask.

The cached nature of neither is guaranteed to remain constant, but as implementation-dependent optimisations that are only implementation-dependent as optimisations (that is, they'd still work correctly if the implementation changed to something that was still valid) the use of Task.Delay(0) was better than the accepted answer.