CODEWITHSUNDEEP
c#multithreadingtask
MRebai
MRebai

Reputation: 5474

action: specifier Task C#

While I was working with Tasks I come across this syntax: 

class Program
{
    static void TestMethod()
    {
        Console.WriteLine("Test");
    }

    static  void Main(string[] args)
    {
        Task t = Task.Run(action: TestMethod); // Why this action: specifier
        t.Wait();
        Console.ReadKey();
    }
}

If I remove the action keyword, the compiler give me an error message that say :

error CS0121: The call is ambiguous between the following methods or properties: 'System.Threading.Tasks.Task.Run(System.Action)' and 'System.Threading.Tasks.Task.Run(System.Func)'

Actually, it's weird to get this kind of message since we don't have a return Type for the method that we pass, thus it should be treated as Action instead of Func<>.

I know there are many other ways to fix that error like casting to Action or anonymous method. However, I can't understand where does this action: come from and it's working.

Upvotes: 0

Views: 78

Answers (2)

MarkusParker
MarkusParker

Reputation: 1596

This is called named arguments. It a feature of the c# language which allows to specify the arguments of a function call in an arbitrary order by specifing their name. For more information see [https://msdn.microsoft.com/en-us/library/dd264739.aspx]. In your case it makes the call of Run unique, because only the System.Threading.Tasks.Task.Run(System.Action) variant has a parameter called action.

Upvotes: 4

No&#233;mie Lord
No&#233;mie Lord

Reputation: 781

action: is the name of the parameter. Here, you are basically telling the compiler : here is something, now I want you to put it in the parameter that's called 'action'. Since in this case the 2 methods don't have the same parameter name, the compiler is able to understand which one you want to call, hence why you get the error without it.

Side note : this can also be used to give parameters out of order when calling a function, or to specify only some optional parameter while ignoring the other ones before. Pretty cool feature sometimes.

Upvotes: 0

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