What Is Subtyping?

Subtypes are the cool kids of programming language theory. They're like the nerds at school who always have their noses in a book, but they're also what you want on your trivia team. They're also similar to supertypes, but we'll get to that later. Let's talk about what subtypes are and how they work. Subtyping is a data type related to a supertype based on the concept of substitutability in programming language theory, where program components such as functions and subroutines made for the supertype will still run if given the subtype. Subtypes are integral to object-oriented programming and are substitutable to supertypes with even more stringent specifications. If necessary, Subtyping is the best way to reuse code. It's like a subprime mortgage: it seems like a good idea at first, but you end up with more problems than you started with. Subtyping is a technique used in object-oriented programming languages to prevent the copying of redundant code, increase code readability, and avoid bugs by substituting large amounts of similar code with a subtype. A subtype is a sort of object that can satisfy all the requirements of its supertype and more. For instance, B is a subtype of A, which means that B can always be used as a substitute for A, and any constraints imposed on A must also be set on B. This approach relies on the developer following strict rules about what constitutes a valid subtype, which leads to bugs when those rules need to be followed correctly. For example, if we have an animal interface (which has only one method called eat), we can create several classes that implement this interface. One class could be Dog which has two ways called fetch and fetch_again; another could be Cat which has only one method called meow; and so on.