Create Task without lambda

Question

Trying to pass function instead lambda expression and finally mixed up why line:

int t2 = await Task.Run( ()=>Allocate2() );

not raises error. This lambda expression ()=>Allocate2() not returns Task. Why no error?

How to create task without lambda expression with function Allocate?

 static async void Example() { int t = await Task.Run(Allocate); int t2 = await Task.Run( ()=>Allocate2() ); Console.WriteLine("Compute: " + t); } static Task<int> Allocate() { return 1; } static int Allocate2() { return 1; }

Task.Run return Task. What this task is doing inside is another story (see overloads). — Sinatr
– Sinatr, Commented Sep 25, 2017 at 12:07
running this I get this error Cannot implicitly convert type 'int' to 'System.Threading.Tasks.Task<int>' because your return type isnt matched. but what is it that you are trying to acheive. — Simon Price
– Simon Price, Commented Sep 25, 2017 at 12:12
why don't you make Allocate async and call var t = await Allocate(); — Gabriel
– Gabriel, Commented Sep 25, 2017 at 12:24

Matthew Watson · Accepted Answer · 2017-09-25 12:24:47Z

Task.Run() wants you to pass a parameterless Action or Func to it.

A lambda can be assigned to an Action or a Func (as appropriate) which is why calling Task.Run() with a lambda works for you.

If you don't want to use a lambda, you must explicitly create an Action or a Func, passing the method you want to call to the constructor of the Action or the Func.

The following demonstrates:

static void Main() { var task = Task.Run(new Action(MyMethod)); } static void MyMethod() { Console.WriteLine("MyMethod()"); }

OR:

static void Main() { var task = Task.Run(new Func<int>(MyMethod)); } static int MyMethod() { Console.WriteLine("MyMethod()"); return 42; }

Note that this doesn't work if the method needs one or more parameters. In that event, you must use a lambda.

You could also perform an explicit cast as an alternative to newing.
@vico You can cast it like so: var task = Task.Run((Func<int>)MyMethod); - but I don't really think that is an improvement. It actually ends up with more or less the same generated code. (See here for more info)

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