is it possible to create a generic closure in Swift?

Question

func myfunc(i:T) -> T {
    return i
}

is it possible to make this generic function a closure?

let myfunc = {          


        

Answer 1

As mentioned, variables in Swift cannot be generic, so creating a closure, whose generic types are specified by the caller is not possible. However, there are workarounds:

With SE-253, it is possible to make arbitrary (nominal) types callable. So instead of declaring a generic closure, we can declare a (non-generic) struct that has a generic callAsFunction method:

struct MyFunc {
    func callAsFunction(_ i: T) -> T {
        return i
    }
}

Now, we can declare a non-generic variable that we can call with a generic value:

let myFunc = MyFunc()
let x = myFunc(42) // -> Int
let y = myFunc("foo") // -> String

Note that this workaround doesn't apply to all situations, but it can be helpful in some.