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Check if Action is async lambda

Tags:

c#

async-await

Since I can define an Action as

Action a = async () => { };

Can I somehow determine (at run time) whether the action a is async or not?

like image 585
David Božjak Avatar asked Sep 26 '13 09:09

David Božjak


2 Answers

No - at least not sensibly. async is just a source code annotation to tell the C# compiler that you really want an asynchronous function/anonymous function.

You could fetch the MethodInfo for the delegate and check whether it has an appropriate attribute applied to it. I personally wouldn't though - the need to know is a design smell. In particular, consider what would happen if you refactored most of the code out of the lambda expression into another method, then used:

Action a = () => CallMethodAsync();

At that point you don't have an async lambda, but the semantics would be the same. Why would you want any code using the delegate to behave differently?

EDIT: This code appears to work, but I would strongly recommend against it:

using System;
using System.Runtime.CompilerServices;

class Test
{
    static void Main()        
    {
        Console.WriteLine(IsThisAsync(() => {}));       // False
        Console.WriteLine(IsThisAsync(async () => {})); // True
    }

    static bool IsThisAsync(Action action)
    {
        return action.Method.IsDefined(typeof(AsyncStateMachineAttribute),
                                       false);
    }
}
like image 118
Jon Skeet Avatar answered Nov 18 '22 06:11

Jon Skeet


Of course, You can do that.

private static bool IsAsyncAppliedToDelegate(Delegate d)
{
    return d.Method.GetCustomAttribute(typeof(AsyncStateMachineAttribute)) != null;
}
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Sriram Sakthivel Avatar answered Nov 18 '22 05:11

Sriram Sakthivel