Overload resolution and async await

Question

Below code gives error CS0121,

The call is ambiguous between the following methods or properties: 'RunTask(System.Func<System.Threading.Tasks.Task>)' and 'RunTask(System.Action)'

static void RunTask(Func<Task> intTask)
{
}

static void RunTask(Action voidTask)
{
}

static async Task DoAsyncTask()
{
    await Task.Delay(500);
}

public static void Main(string[] args)
{
    var asyncTask = new Func<Task>(DoAsyncTask);
    RunTask(DoAsyncTask);
}

But below code can compile

static void RunTask(Func<Task> intTask)
{
}

static void RunTask(Action voidTask)
{
}

static async Task DoAsyncTask()
{
    await Task.Delay(500);
}

public static void Main(string[] args)
{
    var asyncTask = new Func<Task>(DoAsyncTask);
    RunTask(asyncTask);
}

Why so?

score 3 · Accepted Answer · edited May 23 '17 at 12:28

3

The C# compiler does not take return type of a delegate into account when trying to decide the best overloaded method that takes a delegate.

Also see this question

edited May 23 '17 at 12:28

Community

1
1

answered Feb 05 '14 at 14:04

Moeri

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Fair enough, but why a delegate can compile? – imgen Feb 05 '14 at 15:10
Because you've explicitly declared the type of asyncTask to be Func, which makes it easy for the compiler. – Moeri Feb 05 '14 at 15:20

Overload resolution and async await

1 Answers1