Because Spring framework in Swift 2.0 is awesome, lazy functions are moaar awesome !!!

SpringExtension.swift

extension SpringView {

    func fadeIn(duration: CGFloat, completion: (() -> ())? = nil) {
        self.animation = "fadeIn"
        self.duration = duration
        self.animateNext() {
            completion?()
        }
    }

    func fadeOut(duration: CGFloat, completion: (() -> ())? = nil) {
        self.animation = "fadeOut"
        self.duration = duration
        self.animateNext() {
            completion?()
        }
    }
}