import Cocoa class PrimaryWindowController: NSWindowController { // This is used to programmatically control tabs. weak var windowManager: PrimaryWindowManager? // This is required for the "+" button to show up in the tab bar to add a // new tab. override func newWindowForTab(_ sender: Any?) { guard let window = self.window else { preconditionFailure("Expected window to be loaded") } guard let manager = self.windowManager else { return } manager.addNewTab(to: window) } }