Asynchronous software and virtual functions

Question

If I have an interface, for example:

using System.Threading.Tasks; ... public interface IFoo { Task doIt(); Task<bool> doItAndReturnStuff(); } 

and one of the classes that implements this interface simply does not require the use of async methods, how can I fix the redefinition of these functions?

In other words, how to return "void" and "bool" to Task objects correctly?

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 cannot completely remove the Task material, because some classes implementing this interface are actually asynch.

thanks

Answer 1

It is not clear what you are trying to achieve, but one approach (which will be most similar to the "normal" code) is probably just to make them asynchronous methods:

 public async Task DoIt() { // No-op } public async Task<bool> DoItAndReturnStuff() { return true; } 

Without any await expressions, the method will end synchronously anyway. You will receive a warning for each method, but you can only disable it for this piece of code with #pragma .

Alternatively - and I suggest that it’s simpler in terms of not having #pragma turn off warnings — use Task.FromResult :

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