How do I pass a non-awaitable action to a method that takes a Func?

Question

Suppose I have a method as follows...

public static async Task DoIt(Func<Task> doit) {
  // Do something first
  await doit();
  // Do something last
}

I can pass in an awaitable function as follows...

await DoIt(() => Task.Delay(1000));

If I want to pass in something non-awaitable, I can do it like this...

_ = DoIt(() => Task.Run(() => Console.WriteLine("Hi")));

...but this seems quite ugly. Is there a neater way of doing this?

From [a similar question](https://stackoverflow.com/questions/17119075/do-you-have-to-put-task-run-in-a-method-to-make-it-async) it looks like `Task.Run()` is the cleanest way to wrap a synchronous method to return a `Task`. — D M, Oct 31 '22 at 16:38
Anything that returns `Task` is awaitable, so the question may be posed incorrectly. — Jeppe Stig Nielsen, Oct 31 '22 at 16:38
Just mark the lambda `async`, as in: `_ = DoIt(async () => Console.WriteLine("Hi"));` — madreflection, Oct 31 '22 at 16:39
@ewerspej I don't have a problem with it, I'm just trying to look for a cleaner syntax. There's quite a lot of noise in that second call — Avrohom Yisroel, Oct 31 '22 at 16:39
@JeppeStigNielsen Hmm, good point! Thanks for the observation — Avrohom Yisroel, Oct 31 '22 at 16:40
@madreflection Thanks, that's a great suggestion. Do you want to post it as an answer and I'll accept it? — Avrohom Yisroel, Oct 31 '22 at 16:41
@AvrohomYisroel: I suggest accepting John Wu's answer instead. Unlike my glib suggestion, that answer doesn't produce a warning about the lambda being async without awaiting anything. — madreflection, Oct 31 '22 at 16:46
@madreflection True, but yours is neater! Will accept his though. Thanks again — Avrohom Yisroel, Oct 31 '22 at 16:50
Sure, but it's important to clear all warnings, and suppressing them is dirty business. — madreflection, Oct 31 '22 at 16:51
@madreflection Agreed 100%. I'm a bit OCD about warnings myself! — Avrohom Yisroel, Oct 31 '22 at 16:53

score 5 · Accepted Answer · answered Oct 31 '22 at 16:38

If the action is an async, non-awaitable method (e.g. async void) there isn't really a proper way to return a task. There is no way to return a task that signals its completion when the async void method finishes.

If the action is a synchronous method, you can just return Task.CompletedTask.

_ = DoIt(() => { Console.WriteLine("Hi"); return Task.CompletedTask; } );

Theodor Zoulias · Answer 2 · 2022-10-31T18:11:13.077

You could consider adding a DoIt overload that has an Action parameter, and delegates to the primary DoIt(Func<Task>):

public static Task DoIt(Action action)
    => DoIt(() => { action(); return Task.CompletedTask; });

The action is captured by the () => lambda, so this approach has a minuscule overhead (a small object is heap-allocated on each call).

Be aware that the action will be invoked on the context of the caller. It might be invoked on the same thread that invoked the DoIt, and depending on the specifics of the code block // Do something first it might even be invoked synchronously.

How do I pass a non-awaitable action to a method that takes a Func?

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