How to create three random numbers that are not the same in Swift

I am relatively new to Swift and am making a game. I have four integers titled "pos1," "pos2," "pos3," and "pos4." They each have to contain a number from 1 - 4, but each number has to contain a different number (ex. if pos1 = 3, none of the other integers can equal 3). I made a function that does this, but it is not very efficient. Is there a better way of doing this?

My code:

func buildWallType1() {
    var stay = 1
    var pos1 = Int(arc4random_uniform(4) + 1)
    var pos2 = Int(arc4random_uniform(4) + 1)
    var pos3 = Int(arc4random_uniform(4) + 1)
    var pos4 = Int(arc4random_uniform(4) + 1)
    while stay == 1 {
        if pos2 == pos1 || pos2 == pos3 || pos2 == pos4 {
            pos2 = Int(arc4random_uniform(4) + 1)
        }
        else if pos2 != pos1 && pos2 != pos3 && pos2 != pos4 {
            stay = 2
        }
    }
    while stay == 2 {
        if pos3 == pos1 || pos3 == pos2 || pos3 == pos4 {
            pos2 = Int(arc4random_uniform(4) + 1)
        }
        else if pos3 != pos1 && pos3 != pos2 && pos3 != pos4 {
            stay = 3
        }
    }
    while stay == 3 {
        if pos4 == pos1 || pos4 == pos2 || pos4 == pos3 {
            pos2 = Int(arc4random_uniform(4) + 1)
        }
        else if pos4 != pos1 && pos4 != pos3 && pos4 != pos2 {
            stay = 4
        }
    }
}