var buttonLeftConstraint: NSLayoutConstraint?

func pureLayout() {
    buttonLeftConstraint = animateButton.autoPinEdge(toSuperviewEdge: .left, withInset: 20)
    animateButton.autoPinEdge(toSuperviewEdge: .top, withInset: 50)
    animateButton.autoSetDimensions(to: CGSize(width: 100, height: 100))
}

func animate() {
    UIView.animate(withDuration: 1) {
        let random: Double = Double(arc4random_uniform(200))
        self.buttonLeftConstraint?.constant = random
        self.view.layoutIfNeeded()
    }
}

///

var buttonLeftConstraint: NSLayoutConstraint?

func anchorLayout() {
    animateButton.translatesAutoresizingMaskIntoConstraints = false
    buttonLeftConstraint = animateButton.leftAnchor.constraint(lessThanOrEqualTo: view.leftAnchor, constant: 20)
    buttonLeftConstraint?.isActive = true
    animateButton.topAnchor.constraint(equalTo: view.topAnchor, constant: 50).isActive = true
    animateButton.widthAnchor.constraint(equalToConstant: 100).isActive = true
    animateButton.heightAnchor.constraint(equalToConstant: 100).isActive = true
}

func animate() {
    UIView.animate(withDuration: 1) {
        let random: CGFloat = CGFloat(arc4random_uniform(200))
        self.buttonLeftConstraint?.constant = random
        self.view.layoutIfNeeded()
    }
}