Example code for article about UndoManager - Managing a History Part 2

HistoryService.swift

class HistoryService {

    // ...

    // 4
    func registerUndoFor(command: Command) {
        undoManager.registerUndo(withTarget: self) { selfTarget in
            command.isUndone = true
            command.reverse()
            selfTarget.registerRedoFor(command: command)
        }
    }

    // 5
    func registerRedoFor(command: Command) {
        undoManager.registerUndo(withTarget: self) { selfTarget in
            command.isUndone = false
            command.execute()
            selfTarget.registerUndoFor(command: command)
        }
    }
    
    // ...
}