When a class inherits from another class, it inherits all the elements that compose the parent class, which is also known as a superclass. The class that inherits the elements is known as a subclass. For example, the
Mammal subclass inherits all the properties, instance fields or instance attributes, and class fields or class attributes defined in the
Animal abstract class is the baseline for our class hierarchy. We say that it is an abstract class because we shouldn't create instances of the
Animal class; instead, we must create instances of the specific subclasses of
Animal. However, we must take into account that Swift doesn't allow us to declare a class as an abstract class.
We require each