We have already had a general introduction to how generic types work when we looked at Swift arrays and dictionaries. A generic type is a class, structure, or enumeration that can work with any type, just like the way the Swift arrays and dictionaries work. As we recall, Swift arrays and dictionaries are written so that they can contain any type. The catch is we cannot mix-and-match different types within an array or dictionary. When we create an instance of our generic type, we define the type that the instance will work with. After we define that type, we cannot change the type for that instance.
To demonstrate how to create a generic type, let's create a simple List class. This class will use a Swift array as the backend storage for the list and will let us add items to the list or retrieve values from the list.
Let's begin by seeing how to define our generic list type:
class List<T> {
}
The preceding code defines the generic list type. We can see that we...