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 | public extension UIView {public func addOverlay(_ subView: UIView) {
 addConstraints(subView, l: 0, r: 0, t: 0, b: 0)
 }
 
 public func addConstraints(_ subView: UIView, l:CGFloat? = nil, r: CGFloat? = nil, t: CGFloat? = nil, b:CGFloat? = nil, h: CGFloat? = nil, w: CGFloat? = nil, cx: CGFloat? = nil, cy: CGFloat? = nil) {
 addSubview(subView)
 subView.translatesAutoresizingMaskIntoConstraints = false
 
 if let l = l {
 subView.leadingAnchor.constraint(equalTo: leadingAnchor, constant: l).isActive = true
 }
 if let r = r {
 subView.trailingAnchor.constraint(equalTo: trailingAnchor, constant: r).isActive = true
 }
 if let t = t {
 subView.topAnchor.constraint(equalTo: topAnchor, constant: t).isActive = true
 }
 if let b = b {
 subView.bottomAnchor.constraint(equalTo: bottomAnchor, constant: b).isActive = true
 }
 if let h = h {
 subView.heightAnchor.constraint(equalToConstant: h).isActive = true
 }
 if let w = w {
 subView.widthAnchor.constraint(equalToConstant: w).isActive = true
 }
 if let cx = cx {
 subView.centerXAnchor.constraint(equalTo: centerXAnchor, constant: cx).isActive = true
 }
 if let cy = cy {
 subView.centerYAnchor.constraint(equalTo: centerYAnchor, constant: cy).isActive = true
 }
 
 }
 }
 
 |