Xcode-beta (7A176x): If Swift supports type-erased protocols, allow generic Self constraint

Originator:david.w.hart
Number:rdar://22231099 Date Originated:11-Aug-2015 05:09 PM
Status:Open Resolved:
Product:Developer Tools Product Version:Xcode-beta (7A176x)
Classification:Feature (New) Reproducible:Always
 
Given a protocol with an associated type:

protocol Proto {
	typealias T

	let value: T { get }
	init(value: T)
}

If Swift ever allows type-erasure:

let a: Proto<Int> = …

I’d like it if we could use Self generically:

extension Proto<T> {
    func map<U>(transform: T -> U) -> Self<U> {
        return Self.init(transform(self.value))
    }
}

Like this, this map function could be defined to return the same type but with a different generic type.

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