Example code for article about UndoManager - Managing a History Part 3

HistoryService.swift

class HistoryService {
  
    // ...

    // 6
    func record(command: Command) {
        // Remove all undone actions at top of list.
        history = Array(history.drop { $0.isUndone} )
        // Prepend command.
        history = [command] + history
        registerUndoFor(command: command)
        // Execute command.
        command.execute()
    }
}