What is an alternative for Task.FromResult<T>() for tasks that represent operations returning void [duplicate]

Question

What is the best way to return a task that doesn't have a generic type parameter? In other words a task that represents an operation that doesn't return anything or returns void?

In other words, I am looking for alternatives for the following:

T value = default(T);
return Task.FromResult<T>(value); // and

var tcs = new TaskCompletionSource<T>();
tcs.SetResult(value);
return tcs.Task;

But for tasks that represent operations that are not supposed to return anything.

Answer 1

I'm not sure if this is strictly idiomatic, but I use Task.CompletedTask for this. A Task.FromResult is commonly used, but in all scenarios I can think of CompletedTask works identically, and makes more sense semantically.

Answer 2

Task<T> extends Task - so it's reasonably common to just use Task.FromResult<object> and provide an empty result. For example:

Task ret = Task.FromResult<object>(null);

(Or use a value type - it really doesn't matter much.)

Of course, as tasks are immutable you could create a singleton instance of this and return it every time you want to return a completed task. (I believe that's what the async/await infrastructure does, in fact - or at least did in beta releases...)

As Asad noted, you can use Task.CompletedTask, but only if you're targeting .NET 4.6. (Actually, it's not clear whether it's supporting in .NET 4.5 or not - the documentation shows ".NET Framework 4.6 and 4.5" as the version number, but then says "Supported in: 4.6"...)