Programmatic autolayout constraints

Autolayout.swift

// the frame size doesn't matter; autolayout will change it     
var aButton = UIButton(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
aButton.titleLabel?.text = "HEY"
aButton.opaque = true
aButton.backgroundColor = UIColor.yellow
view.addSubview(aButton)
        
aButton.translatesAutoresizingMaskIntoConstraints = false
        
let margins = view.layoutMarginsGuide
        
aButton.trailingAnchor.constraintEqualToAnchor(margins.trailingAnchor, constant: -0).active = true
        
aButton.bottomAnchor.constraintEqualToAnchor(bottomLayoutGuide.topAnchor, constant: -30).active = true
        
aButton.topAnchor.constraintEqualToAnchor(topLayoutGuide.bottomAnchor,  constant: 8.0).active = true