How can I make a extension for array of specific type in Swift

Question

for say I have:

struct S {
    var num = 0
}

I wanna implement a function allEqual() as extension for Array<S>, so I could do thing like

var s1 = S()
var s2 = S()
var s3 = S()
var equality = [s1,s2,s3].allEqual()

Answer 1

for say the specific type is S

extension CollectionType where Generator.Element == S {
}

CollectionType Protocol

Answer 2

In the latest Swift 3.1. You can do same-type constraints on the concrete type extension. So in your case, you can do:

extension Array where Element == S {
    func allEqual() -> Bool {
        ...
    }
}