Question

If I have an interface such as:

using System.Threading.Tasks;

...

public interface IFoo
{
  Task doIt();

  Task<bool> doItAndReturnStuff();
}

and one of the classes implementing this interface just happens to not require async methods, how can i correct override these functions?

In other words, how do I correctly return “void” and “bool” wrapped in Task objects?

For example:

public class FooHappensToNotNeedAsync : IFoo
{
  public override Task doIt()
  {
    // If I don't return anything here, I get
    // error that not all code paths return a value.
    // Can I just return null?
  }

  public override Task<bool> doItAndReturnStuff()
  {
    // If I want to return true, how to I do it?
    // This doesn't work:
    return true;
  }
}

NOTE – I can’t strip the Task stuff completely because some of the classes that implement this interface are in fact asynch.

Thanks

Answer 1

It’s not clear what you’re trying to achieve, but one approach (which would look the most like “normal” code) is probably just to make them async methods anyway:

public async Task DoIt()
{
    // No-op
}

public async Task<bool> DoItAndReturnStuff()
{
    return true;
}

Without any await expressions, the method will complete synchronously anyway. You’ll get a warning on each method, but you could disable that just for this piece of code using a #pragma.

Alternatively – and I guess more simply in terms of not requiring a #pragma to disable warnings – would be to use Task.FromResult:

public Task DoIt()
{
    // Returns a Task<bool>, but that's okay - it's still a Task
    return Task.FromResult(true);
}

public Task<bool> DoItAndReturnStuff()
{
    return Task.FromResult(true);
}