[swift-evolution] [Discussion] Seal `T.Type` into `Type<T>`

Adrian Zubarev adrian.zubarev at devandartist.com
Fri Jul 8 15:06:21 CDT 2016

Hello Swift community, before Swift 3 drops I’d like to discuss if it is reasonable to consider to create a standalone type to drop/seal the T.Type magic?

However this change does not play well with the proposal of dropping the .self compiler magic.

Some bikeshedding:

public struct Type<T> : Hashable {
    // Seal the `.Type` magic into this standalone type.
    // Disallow `.Type` usage elsewhere
    public let sealed: T.Type
    public var hashValue: Int { /* implement somehow */ }
    public init() {
        // Or do it somehow different for the sake of dropping `.self` magic
        self.sealed = T.self

public func ==<T>(lhs: Type<T>, rhs: Type<T>) -> Bool {
    return lhs.hashValue == rhs.hashValue
Downside of this approach is the accessibility of the .Type instance:

protocol Initializable {

func foo<T : Initializable>(type: Type<T>) -> T {
    // It would be nice if we could use `type.init()` instead, but than we
    // would need more compiler magic :/
    return type.sealed.init()
I couldn’t come up with a better name than sealed, if anyone has a better idea feel free to share your thoughts.

Remember this is a discussion and not (yet) a detailed proposal, where everyone can provide feedback and bikeshedding for a better design.

Adrian Zubarev
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