SwiftyConstraints is and extension of the UIView class that enable every instance of the UIView's sub classes (UILabel, UIButton, etc) to set constraints programmatically between two UIView(or sub classes) in a Swifty way :)
In this case, the label that we create will be centered to the main view
let lbl = UILabel()
lbl.setConstraint(pinTo: self.view, constraintType: .fixedSizeConstrainToCenter)