Looking at that proposal on Austin’s Github, would its complete implementation
require/allow for any type that’s known at runtime to be used like a type at
compile time? So that these two blocks would both work? It seems like the
runtime would be using the same technology, but it’s hard to tell.
let a : Collection where .Element == Int = // ...
let b : Collection where .Element == Int = // ...
func someGenericFunc<C : Collection>(x: C, y: C) where C.Element == Int {
// ...
}
if let openedA = a as? a.Self, let openedB = b as? a.Self {
// openedA is type a.Self; openedB is type a.Self
// We now know that openedA and openedB are the same concrete type, which
// conforms to Collection with Elements that are Ints
// This is okay
someGenericFunc(x: openedA, y: openedB)
}
let a : Collection where .Element == Int = // ...
let b : Collection where .Element == Int = // ...
func someGenericFunc<C : Collection>(x: C, y: C) where C.Element == Int {
// ...
}
let desiredType = type(of: a)
if let openedA = a as? desiredType, let openedB = b as? desiredType {
// openedA is type a.Self; openedB is type a.Self
// We now know that openedA and openedB are the same concrete type, which
// conforms to Collection with Elements that are Ints
// This is okay
someGenericFunc(x: openedA, y: openedB)
}
assert(type(of: a) === a.Self.self)
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