This tutorial is the second installment in an AppCoda series on design patterns started last week. There are 23 classic software development design patterns probably first identified, collected, and explained all in one place by the “Gang of Four” (“GoF”), Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides in their seminal book, “Design Patterns: Elements of Reusable Object-Oriented Software.”. Today, we’ll focus on two of these patterns, “observer” and “memento,” which fall into what the GoF calls the “behavioral” category.
