Hands-On Design Patterns with Swift

Implementing the memento pattern

Let's imagine you are building an app that manages a shopping list. On the fly, users can add new items, edit items, and also mark them as done (picked up in-store).

Each element of the shopping list can be represented as an Item object:

struct Item {var name: String    var done: Bool = false}

Again, we'll use a struct, as for the memento pattern we want all the features of value types such as immutability and copy-on-write.

Then we need to represent the Originator, Memento, and CareTaker objects.

A shopping list is just a list. For the sake of our example, we can implement it in many ways, wrapping the list into a ShoppingList as the OriginatorType, using [Item] as the MementoType, or introducing a third object ...