Is it possible to declare an empty function as a variable in Swift?

Question

Is it possible to do something like this, and create an empty function that will later be assignable, because I keep getting an error where i can't call the function that was assigned this is the closest I have gotten

fileprivate class actionButton: UIButton{
    var functo = ()
    func tapped(functoCall: () ->Void){
        self.functo()
    }
}

this buttons initialized in a function which takes a function as a parameter and passes it on to this button which is a descendent of the class specified above

    button.functo = funcToCall()
    button.addTarget(self, action: #selector(yes.tapped(functoCall:)), for: .touchDown)

the issue i get is when i try to call self.functo() i get cannot call non-function type

Answer 1

Yes that is possible.

The reason you are getting the error is that the compiler can't know that functo is in fact a function that is callable. You made it an Any implicitly.

You just have to cast it (using if let for example) to a function of the desired type first.

Something like this should get you started:

var myfunc: Any = ()

func test() -> String {
    return "Cool"
}
// Assign any function to myfunc
myfunc = test

// Just cast it to the expected type
if let x = myfunc as? ()->String {
    x()
}

In case the question is just particular to this problem (as a downvoter thinks) you can just type your variable with the signature of your function. This is the trivial case:

var myfunc: ((Any) -> Void)? = nil

Then it is callable when you assign it.