I first wrote about multiple-index arrays a year ago. Yesterday, someone was asking about them again so I updated my code for Swift 2.0

extension Array {
    typealias ArrayType = Element
    subscript(i1: Int, i2: Int, rest: Int...) ->  [ArrayType] {
        get {
            var result : [Element] = [self[i1], self[i2]]
            for index in rest {
                result.append(self[index])
            }
            return result
        }

        // Thanks Big O Note Taker
        set (values) {
            for (index, value) in zip([i1, i2] + rest, values) {
                self[index] = value
            }
        }
    }
}

Not a huge change. Just really needed to tweak append and I added an explicit type for the result array. Update: Added the setter as suggested.

let foo = [1, 2, 3, 4, 5, 6, 7]
println(foo[2]) // prints 3
println(foo[2, 4]) // prints [3, 5]
println(foo[2, 4, 1]) // prints [3, 5, 2]
println(foo[2, 4, 1, 5]) // prints [3, 5, 2, 6]

The setter runs out when the values do, so if you set alphabet[2, 3, 5] = ["X1", "X2"], only indices 2 and 3 get updated.