protocol ValueForKeyLookupable {
    func valueForKey(key: String) -> Any?
}

extension ValueForKeyLookupable {
    func valueForKey(key: String) -> Any? {
        let mirror = reflect(self)
        for index in 0..<mirror.count {
            let child = mirror[index]
            if key == child.0 {return child.1.value}
        }
        return nil
    }
}

struct Pt: ValueForKeyLookupable {
    let x: Int
    let y: Int
    init(_ x: Int, _ y: Int) {self.x = x; self.y = y}
    init(){self.init(0, 0)}
}

let p = Pt(2, 3)

p.valueForKey("x")
p.valueForKey("y")