Swift 4 UIView Autolayout extensions.

UIView+AutoLayout.swift

extension UIView {
    @discardableResult
    public func constrainEdges(to view: UIView) -> [NSLayoutConstraint] {
        let constraints = [
            leadingAnchor.constraint(equalTo: view.leadingAnchor),
            topAnchor.constraint(equalTo: view.topAnchor),
            trailingAnchor.constraint(equalTo: view.trailingAnchor),
            bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ]
        NSLayoutConstraint.activate(constraints)
        return constraints
    }
    
    @discardableResult
    public func constrainEdges(toMarginOf view: UIView) -> [NSLayoutConstraint] {
        let margins = view.layoutMarginsGuide
        let constraints = [
            leadingAnchor.constraint(equalTo: margins.leadingAnchor),
            topAnchor.constraint(equalTo: margins.topAnchor),
            trailingAnchor.constraint(equalTo: margins.trailingAnchor),
            bottomAnchor.constraint(equalTo: margins.bottomAnchor)
        ]
        NSLayoutConstraint.activate(constraints)
        return constraints
    }
    
    @discardableResult
    public func center(in view: UIView) -> [NSLayoutConstraint] {
        let constraints = [
            centerXAnchor.constraint(equalTo: view.centerXAnchor),
            centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ]
        NSLayoutConstraint.activate(constraints)
        return constraints
    }
}