Using a Type Variable in a Generic

Question

I have this question except for Swift. How do I use a Type variable in a generic?

I tried this:

func intType() -> Int.Type {
    retu         


        

Answer 1

Its possible so long as you can provide "a hint" to the compiler about the type of... T. So in the example below one must use : String?.

func cast(_ value: Any) -> T? {
    return value as? T
}

let inputValue: Any = "this is a test"
let casted: String? = cast(inputValue) 
print(casted) // Optional("this is a test")
print(type(of: casted)) // Optional

Why Swift doesn't just allow us to let casted = cast(inputValue) I'll never know.

---

One annoying scenerio is when your func has no return value. Then its not always straightford to provide the necessary "hint". Lets look at this example...

func asyncCast(_ value: Any, completion: (T?) -> Void) {
    completion(value as? T)
}

The following client code DOES NOT COMPILE. It gives a "Generic parameter 'T' could not be inferred" error.

let inputValue: Any = "this is a test"
asyncCast(inputValue) { casted in
    print(casted) 
    print(type(of: casted))
}

But you can solve this by providing a "hint" to compiler as follows:

asyncCast(inputValue) { (casted: String?) in
    print(casted) // Optional("this is a test")
    print(type(of: casted)) // Optional
}