How to be Lazy in Extensions - Solution

how-to-be-lazy-in-extensions.swift

public extension UIView {

    private struct AssociatedKey {
        static var constrictor: UInt8 = 0
    }

    var constrictor: Constrictor {
        if let constrictor = objc_getAssociatedObject(self, &AssociatedKey.constrictor) as? Constrictor {
            return constrictor
        } else {
            let constrictor = Constrictor(object: self)
            objc_setAssociatedObject(self, &AssociatedKey.constrictor, constrictor, .OBJC_ASSOCIATION_RETAIN)
            return constrictor
        }
    }
}