NSControl extension for closure version of `.action`

NSControl+Extension.swift

enum AssociationPolicy {
	case assign
	case retainNonatomic
	case copyNonatomic
	case retain
	case copy

	var rawValue: objc_AssociationPolicy {
		switch self {
		case .assign:
			return .OBJC_ASSOCIATION_ASSIGN
		case .retainNonatomic:
			return .OBJC_ASSOCIATION_RETAIN_NONATOMIC
		case .copyNonatomic:
			return .OBJC_ASSOCIATION_COPY_NONATOMIC
		case .retain:
			return .OBJC_ASSOCIATION_RETAIN
		case .copy:
			return .OBJC_ASSOCIATION_COPY
		}
	}
}

final class ObjectAssociation<T: Any> {
	private let policy: AssociationPolicy

	init(policy: AssociationPolicy = .retainNonatomic) {
		self.policy = policy
	}

	subscript(index: AnyObject) -> T? {
		get {
			// Force-cast is fine here as we want it to fail loudly if we don't use the correct type.
			// swiftlint:disable:next force_cast
			objc_getAssociatedObject(index, Unmanaged.passUnretained(self).toOpaque()) as! T?
		}
		set {
			objc_setAssociatedObject(index, Unmanaged.passUnretained(self).toOpaque(), newValue, policy.rawValue)
		}
	}
}


extension NSControl {
	typealias ActionClosure = ((NSControl) -> Void)

	private struct AssociatedKeys {
		static let onActionClosure = ObjectAssociation<ActionClosure>()
	}

	@objc
	private func callClosure(_ sender: NSControl) {
		onAction?(sender)
	}

	/**
	Closure version of `.action`.

	```
	let button = NSButton(title: "Unicorn", target: nil, action: nil)

	button.onAction = { sender in
		print("Button action: \(sender)")
	}
	```
	*/
	var onAction: ActionClosure? {
		get {
			return AssociatedKeys.onActionClosure[self]
		}
		set {
			AssociatedKeys.onActionClosure[self] = newValue
			action = #selector(callClosure)
			target = self
		}
	}
}

error: use of unresolved identifier 'AssociatedObject'
        static let onActionClosure = AssociatedObject<ActionClosure>()

Fixed