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About JS: Polymorphism

OOP is a hard concept to formalize and has many aspects. OOP has been understood to mean different things at different times. There are at least two kinds of OOP: one formulated by Alan Kay, the creator of SmallTalk, and another, about polymorphism, inheritance, and encapsulation (Grady Butch). In today's world, OOP usually refers to the latter, although the former is alive and well in many languages. But even when we talk about the second kind of OOP, different languages still emphasize different features. What is considered a sign of true OOP in some languages is unacceptable in others.

If we try to generalize somehow and find the most fundamental thing that all OOP languages have (according to Butch), most likely the common point of contact will be polymorphism of subtypes.

Polymorphism (of subtypes) is probably the most important feature of modern object-oriented programming. Benjamin Pierce. Author of “Types and Programming Languages”.

In this course, we will take an in-depth look at polymorphism, the mechanisms of its implementation and, most importantly, learn how to apply it correctly. The main topics of this course are:

  • Types of polymorphism: subtype and parametric
  • Dispatching and types of dispatching
  • Dependency inversion and injection
  • DI container
  • SOLID (SRP, OCP, LSP, ISR, DIP)

In addition, we'll get acquainted with the concept of "design patterns". Let's analyze their influence on code structure and get acquainted with some popular ones:

  • Null Object
  • Strategy
  • Factory

Let's talk about when polymorphism is necessary and when it isn't, or when it can even be harmful. We'll look at several techniques that allow you to get polymorphic behavior without using objects. To do this, we'll look at the different types of dispatching.


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