Can `Never` be extended to mark parameters, stored properties etc. as not existing?

Evolution Discussion
21

For more intuition on the difference between Void and Never, consider a function with no return declaration. It is not strictly non-returning, although often named such, but rather void-returning. I guess one could call it a no value-returning function.

func foo() { }

It returns, so therefore it returns something, but that something is kinda like nothing. It is something with no information. The global singleton, which means everything and nothing.

In a sense, Never is loading more information than Void.

I think it is possible to infer default generic type parameters by providing a default value to an initializer now:

struct Product<A, B> {
    var a: A
    var b: B

    init (a: A, b: B = ()) {
        self.a = a
        self.b = b
    }
}

let p = Product(a: 10) // inferred as Product<Int, Void>
p.b // returns (), aka no additional information.
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