How do I immediately return a result from a task

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In a base class, I am trying to create a default implementation for a function returning Task<string>. I can work out how to do this 'long-hand' but I can't help thinking there is a neater way of writing this.

This is my current version:

protected virtual async Task<string> MyFunction()
{
    await Task.Delay( 0 );
    return "";
}

What I have tried:

I thought I might be able to use TaskCompletionSource or Task.FromResult() but don't seem to be able to work out a syntax for these. When using the latter, I can't get round a message that tells me I should be returning a string, not a Task<string>.

Posted 1-Oct-19 1:01am

Patrick Skelton

Updated 1-Oct-19 1:18am

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#realJSOP · Accepted Answer · 2019-10-01T01:18:00

Solution 2

You can just return String.Empty without doing the await. Of course, that would make the method synchronous (because there's no await statement), but I don't see that as a bad thing if it's merely a default implementation.

Posted 1-Oct-19 1:18am

#realJSOP

Updated 1-Oct-19 1:19am

v2

Comments

Patrick Skelton 1-Oct-19 7:23am

Doesn't that mean you are forever stuck with the compiler warning telling you that the task will complete synchronously?

#realJSOP 1-Oct-19 7:27am

Not if you turn off that warning for that method:

#pragma warning disable CS1633,CS1998
public async Task<string>....
{
}
#pragma warning restore CS1633,CS1998

Patrick Skelton 1-Oct-19 7:30am

Not fond of turning off warnings (since in my case, the warning is usually right and I've got my brain in neutral), but thanks for the reply.

#realJSOP 1-Oct-19 7:36am

You can do it around just the offending method (I cahnged my reply to illustrate). Of course, you can put await in the method and be done with it.

#realJSOP 1-Oct-19 7:37am

And, the language gives you the #pramga directive just for situations like this. I don't use them either unless necessary. In this case, it's a do-nothing default implementation of a method. It ain't gonna hurt anything...

#realJSOP 1-Oct-19 7:39am

Your other option is to make the class that contains the default implementation an abstract class, and make the method abstract.

Richard Deeming · Accepted Answer · 2019-10-01T01:16:00

Solution 1

Simple - just remove the async keyword:

C#

protected virtual Task<string> MyFunction()
{
    return Task.FromResult(string.Empty);
}

If your task completes synchronously most of the time, you might want to consider using ValueTask instead.

Understanding the Whys, Whats, and Whens of ValueTask | .NET Blog[^]

Posted 1-Oct-19 1:16am

Richard Deeming

Updated 1-Oct-19 1:17am

v2

Comments

Patrick Skelton 1-Oct-19 7:24am

Wasn't aware of ValueTask at all, so I've learnt two things! Thank you, Richard.

#realJSOP 1-Oct-19 7:54am

Yep, this is the answer. My approach doesn't inherit well. At all. :)