Implementing the Memento Design Pattern for Persistent Object States

The Memento Design Pattern is a common solution in software development for implementing undo/redo functionality. It allows for the preservation of an object's state at a particular point in time, so that it can be restored later. This is especially useful in situations where a user may want to undo or redo actions within an application.

In Swift, the Memento Design Pattern can be implemented using a Memento class that stores the state of an object, as well as a Caretaker class that manages a stack of Memento objects. The Caretaker class is responsible for creating Memento objects and storing them on the stack, as well as providing methods for undoing and redoing actions.

Here is an example of how the Memento Design Pattern could be implemented in Swift for a simple drawing application:

In the example above, the Caretaker class maintains two stacks - one for undo actions and one for redo actions. When a new state is saved, it is added to the undo stack and the redo stack is cleared. The undo and redo methods simply pop the last element off of their respective stacks and return it, while also moving the popped Memento object to the other stack.

Here is an example usage of the code:

The Memento Design Pattern allows for a clean and efficient way to implement undo/redo functionality in Swift. It separates the responsibility of storing an object's state from the object itself, which allows for easy restoration of previous states without the need for complex logic within the object itself.