The AbstractAnimal protocol requires two type methods: printALeg and printAChild. As explained with the type property requirements, we can only use the static keyword to specify a type method requirement, but we can use either static or class when we implement the type method in the class that conforms to the protocol. The usage of the static keyword doesn't have the same meaning that this keyword has when we use it in classes; that is, we can still declare type methods that can be overridden in the classes that conform to the protocol by declaring them with the class keyword in the respective classes. The following line shows the type method requirement for printALeg:
static func printALeg()
The protocol defines three parameterless methods: printLegs, printChildren, and printAge. The method requirements use the func keyword followed by the method name and its arguments, as if we were writing the method declaration for a class but without the method body...
