[Pitch] Use “some” to express “some specialization of a generic type”

[anon9791410]

I'm starting to recognize that people want the any variant of this, as well as the some one.

Why can't I cast `Woo<Any>` to `Woo<Int>` concrete type? But `Array<Any>` to `Array<Int>` is OK?

In Swift, we can cast a type of Array<Any> to Array<Int> if the underlying type is in fact a Array<Int>: let anyArray = [1,2,3] as Array<Any> let arrayActual = anyArray as! Array<Int> // Ok But if I try the same thing with my own generic types, I get a warning from the compiler: Cast from 'Woo<Any>' to unrelated type 'Woo<Int>' always fails and a runtime crash: struct Woo<Boo> { let boo: Boo } let anyWoo = Woo(boo: 3) as Woo<Any> let wooActual = anyWoo as! Woo<Int> // Crash What am I m…

Erasing (or mapping) value type parameters

i have a struct, let’s call it DriverOptions<T> that has a type parameter, and lots and lots of stored properties: @frozen public struct DriverOptions<Authentication> where Authentication:AuthenticationMode { public var authentication:Authentication? public var connectionTimeout:Milliseconds public var replicaSet:String? public var tls:Bool? ... the type parameter is needed when building the DriverOptions instance itself, but now i want to store it insi…

Typealias conformance to protocols, why can't this simple thing be implemented?

It's something like that, but not that. If you don't specify, the class constraint is assumed. (UIView in this case.) class MyViewDelegate: MyDelegate<UIView> { override func getView() -> UIView { .init() } } class MyTableViewDelegate: MyDelegate<UITableView> { override func getView() -> UITableView { .init() } } getViewIfPossible(delegate: MyViewDelegate()) // UIView?.some getViewIfPossible(delegate: MyTableViewDelegate()) // UIView?.none So, just switch to a protocol: protocol Delega…