Function as parameter in async method

Question

I call a method containing a function:

public void DoMagicStuff(Func<T> anyfunction) {
  // do lots of magic stuff
}

This works:

public void DoNonAsyncStuff() {
  DoMagicStuff(()=> {
     AnotherFunction();
  }
}

While this does not:

public async Task<CustomClass> DoAsynStuff() {
   DoMagicStuff(()=> {
     return await DoSomethingDifferent();
  }
}

"The await operator can only be used in async functions"

How do I make this work for async methods?

Answer 1

If you intend to pass asynchronous delegates to DoMagicStuff, then you need to overload that with an asynchronous version:

public void DoMagicStuff(Func<T> anyfunction)
{
    // do lots of magic stuff
    T t = anyfunction();
}

public async Task DoMagicStuff(Func<Task<T>> asyncfunction)
{
    // do lots of magic stuff
    T t = await asyncfunction();
}

This allows you to call await for the asyncfunction.

Any common logic can always be refactored into another method.

---

With regard to your question, await can only be used in a function that has been declared async, which your lambda hasn't.

It should be like this:

public async Task<CustomClass> DoAsynStuff()
{
    await DoMagicStuff(async () =>
    {
        return await DoSomethingDifferent();
    });
}

And in fact, because DoSomethingDifferent already returns a Task, the lambda is superfluous:

public async Task<CustomClass> DoAsynStuff()
{
    await DoMagicStuff(DoSomethingDifferent);
}