UpdateConstraints.swift

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: Constraint?

func snapKit() {
    animateButton.snp.makeConstraints { (make) in
        buttonLeftConstraint = make.left.equalTo(self.view).offset(20).constraint
        make.top.equalTo(self.view).inset(50)
        make.size.equalTo(CGSize(width: 100, height: 100))
    }
}

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