I’m building a complex new app entirely with programmatic Auto Layout. It only supports iOS 9 so that means `UIStackView` and `NSLayoutAnchor` exclusively. These two classes have been very handy thus far, in the spirit of composition over inheritance.

CenteringView.swift

final class CenteringView: UIView {
    // MARK: - Initialization
    
    init(contentView: UIView) {
        super.init(frame: .zero)
        
        addSubview(contentView)
        contentView.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activateConstraints([
            centerXAnchor.constraintEqualToAnchor(contentView.centerXAnchor),
            centerYAnchor.constraintEqualToAnchor(contentView.centerYAnchor),
            widthAnchor.constraintGreaterThanOrEqualToAnchor(contentView.widthAnchor),
            heightAnchor.constraintGreaterThanOrEqualToAnchor(contentView.heightAnchor)
        ])
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

MarginView.swift

public final class MarginView: UIView {
    private let margins: UIEdgeInsets
    
    // MARK: - Initialization
    
    public convenience init(layoutMargin: CGFloat, contentView: UIView) {
        self.init(layoutMargins: UIEdgeInsets(top: layoutMargin, left: layoutMargin, bottom: layoutMargin, 
            right: layoutMargin), contentView: contentView)
    }
    
    public init(layoutMargins: UIEdgeInsets, contentView: UIView) {
        margins = layoutMargins
        
        super.init(frame: .zero)
        
        addSubview(contentView)
        contentView.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activateConstraints([
            contentView.topAnchor.constraintEqualToAnchor(layoutMarginsGuide.topAnchor),
            contentView.leadingAnchor.constraintEqualToAnchor(layoutMarginsGuide.leadingAnchor),
            contentView.trailingAnchor.constraintEqualToAnchor(layoutMarginsGuide.trailingAnchor),
            contentView.bottomAnchor.constraintEqualToAnchor(layoutMarginsGuide.bottomAnchor)
        ])
    }

    required public init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    // MARK: - UIView
    
    public override func didMoveToSuperview() {
        super.didMoveToSuperview()
        
        // http://stackoverflow.com/a/34146177
        layoutMargins = margins
    }
}