NSLayoutConstraint+activate.swift

public final class ViewController: UIViewController {

    private lazy var myView = MyView()

    public override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(myView)
        myView.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate(myView, view) { content, parent in
            content.leadingAnchor.constraint(equalTo: parent.leadingAnchor)
            content.trailingAnchor.constraint(equalTo: parent.trailingAnchor)
            content.topAnchor.constraint(equalTo: parent.safeAreaLayoutGuide.topAnchor)
            content.bottomAnchor.constraint(equalTo: parent.bottomAnchor)
        }
    }
}

public extension NSLayoutConstraint {
    static func activate<V1: UIView, V2: UIView>(
        _ view1: V1,
        _ view2: V2, 
        @Builder _ builder: (_ view1: Proxy<V1>, _ view2: Proxy<V2>) -> [NSLayoutConstraint]
    ) {
        builder(Proxy(view1), Proxy(view2)).forEach { constraint in
            constraint.isActive = true
        }
    }

    @_functionBuilder
    struct Builder {
        public static func buildBlock(_ disposables: NSLayoutConstraint...) -> [NSLayoutConstraint] {
            disposables
        }
    }

    @dynamicMemberLookup
    class Proxy<View: UIView> {
        private var view: View

        init(_ view: View) {
            self.view = view
        }

        public subscript<T: LayoutAnchorType>(dynamicMember keyPath: KeyPath<View, T>) -> T {
            view[keyPath: keyPath]
        }

        public subscript(dynamicMember keyPath: KeyPath<View, UILayoutGuide>) -> UILayoutGuide {
            view[keyPath: keyPath]
        }
    }
}

public protocol LayoutAnchorType {}
extension NSLayoutAnchor: LayoutAnchorType {}