What's wrong here?

swift3.swift

func doThing(x: Int, y: Int, z: Int) -> Int {
    return x + y + z
}

class Foo {   
    func doThing(x: Int) {
        doThing(x: x, y: 2, z: 4) // extra argument 'y' in call
    }
}

It appears that this works:

func doThing(x: Int, y: Int, z: Int) -> Int {
    return x + y + z
}

class Foo {

    func doThing(x: Int) -> Int {
        let result = doThing(x:y:z:)(x, 2, 4)
        return result
    }
}