UISearchBar's set_cancelButtonText: ivar is prohibited

Instead of messing around with the undocumented view hierarchy, you can use UIAppearance:

UIBarButtonItem.appearance(whenContainedInInstancesOf: [UISearchBar.self]).title = "Whatever"

Objective-C version:

[[UIBarButtonItem appearanceWhenContainedInInstancesOfClasses:@[[UISearchBar class]]] setTitle:@"CancelText"];