Re http://stackoverflow.com/questions/43855655/variable-was-never-mutated-consider-changing-to-let#43855655

Pillar.swift

func pillarPlacement(x: CGFloat, y: CGFloat) -> CGPoint {
    let pillarX: CGFloat
    let pillarY: CGFloat
    let random = Int(arc4random_uniform(2))
    
    if random == 1 {
        pillarX = x + 39
        pillarY = y - 29
    } else {
        pillarX = x - 40
        pillarY = y - 30
    }
    
    return CGPoint(x: pillarX, y: pillarY)
}

Note, I also replaced arc4random() % 2 with arc4random_uniform(2) as that solves subtle modulo bias problem ofarc4random with % operator.