Is it possible to make an Array extension in Swift that is restricted to one class?

Question

Can I make an Array extension that applies to, for instance, just Strings?

Answer 1

This has already been answered by the three wise-men above ;-) , but I humbly offer a generalization of @Martin's answer. We can target an arbitrary class by using "marker" protocol that is only implemented on the class that we wish to target. Ie. one does not have to find a protocol per-se, but can create a trivial one for using in targeting the desired class.

protocol TargetType {}
extension Array:TargetType {}

struct Foo  {
    var name:String
}

extension CollectionType where Self:TargetType, Generator.Element == Foo {
    func byName() -> [Foo] { return sort { l, r in l.name < r.name } }
}

let foos:[Foo] = ["c", "b", "a"].map { s in Foo(name: s) }
print(foos.byName())