Scala Design Patterns - Second Edition

Code example

In this subsection, we will go through the text editor code one step at a time and see how the memento design pattern could be implemented in Scala.

First of all, let's see the Caretaker, Memento, and Originator traits:

trait Memento[T] {  protected val state: T  def getState(): T = state}trait Caretaker[T] {  val states: mutable.Stack[Memento[T]] = mutable.Stack[Memento[T]]()}trait Originator[T] {  def createMemento: Memento[T]  def restore(memento: Memento[T])}

We have used generics, and this allows us to reuse those traits multiple times when we want to implement the memento design pattern. Now, let's take a look at the specific implementations of the traits that are necessary in our application:

class TextEditor extends Originator[ ...