a.swift

public extension UIView {
    func pinCenter(view: UIView) -> [NSLayoutConstraint] {
        return [
            centerXAnchor.constraint(equalTo: view.centerXAnchor),
            centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ]
    }
    
    func pin(size: CGSize) -> [NSLayoutConstraint] {
        return [
            widthAnchor.constraint(equalToConstant: size.width),
            heightAnchor.constraint(equalToConstant: size.height)
        ]
    }
}