How to simplify anchor with NSLayoutConstraint in iOS

Issue #368

See https://github.com/onmyway133/Omnia/blob/master/Sources/iOS/NSLayoutConstraint.swift

extension NSLayoutConstraint {

    /// Disable auto resizing mask and activate constraints
    ///
    /// - Parameter constraints: constraints to activate
    static func on(_ constraints: [NSLayoutConstraint]) {
        constraints.forEach {
            ($0.firstItem as? UIView)?.translatesAutoresizingMaskIntoConstraints = false
            $0.isActive = true
        }
    }

    static func on(_ constraintsArray: [[NSLayoutConstraint]]) {
        let constraints = constraintsArray.flatMap({ $0 })
        NSLayoutConstraint.on(constraints)
    }

    func priority(_ value: Float) -> NSLayoutConstraint {
        priority = UILayoutPriority(value)
        return self
    }
}

extension Array where Element == NSLayoutConstraint {
    func priority(_ value: Float) -> [NSLayoutConstraint] {
        forEach {
            $0.priority = UILayoutPriority(value)
        }

        return self
    }
}

extension UILayoutGuide {
    func pinEdges(view: UIView, inset: UIEdgeInsets = UIEdgeInsets.zero) -> [NSLayoutConstraint] {
        return [
            leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: inset.left),
            trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: inset.right),
            topAnchor.constraint(equalTo: view.topAnchor, constant: inset.top),
            bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: inset.bottom)
        ]
    }
}

extension UIView {
    func pinEdges(view: UIView, inset: UIEdgeInsets = UIEdgeInsets.zero) -> [NSLayoutConstraint] {
        return [
            leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: inset.left),
            trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: inset.right),
            topAnchor.constraint(equalTo: view.topAnchor, constant: inset.top),
            bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: inset.bottom)
        ]
    }

    func pinCenter(view: UIView, offset: CGPoint = .zero) -> [NSLayoutConstraint] {
        return [
            centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: offset.x),
            centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: offset.y)
        ]
    }

    func padding(view: UIView, _ constant: CGFloat = 0) -> [NSLayoutConstraint] {
        return [
            leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: constant),
            trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -constant)
        ]
    }

    func size(_ constant: CGFloat) -> [NSLayoutConstraint] {
        return [
            widthAnchor.constraint(equalToConstant: constant),
            heightAnchor.constraint(equalToConstant: constant)
        ]
    }

    func size(_ width: CGFloat, _ height: CGFloat) -> [NSLayoutConstraint] {
        return [
            widthAnchor.constraint(equalToConstant: width),
            heightAnchor.constraint(equalToConstant: height)
        ]
    }

    func addSubviews(_ views: [UIView]) {
        views.forEach {
            addSubview($0)
        }
    }
}