The memento pattern

The memento pattern is useful if you need to preserve multiple states of your program or models, which you want to be able to go back or forward to, such as a browsing history or an undo manager.

In this section, we'll implement the memento pattern with a simple example that showcases the different objects required for this pattern.

Components of the memento pattern

The memento pattern requires the implementation of three distinct entities:

• Memento: a representation of the internal state of Originator, which should be immutable
• Originator: the original object that can produce and consume the Memento, in order to save and restore its own state
• CareTaker: an external object that stores and restores a Memento to an Originator

Note

Memento, in other languages, may be implemented as an opaque box so the state can't be mutated. In Swift, we can leverage structs, their immutability, and the fact they are passed by value and not reference. It is critical that different Memento objects...