Object-oriented basics: inheritance, polymorphism, encapsulation, and abstraction

Inheritance

• prototypal inheritance allows an object
• to base itself on another object
• class-based inheritance allows a class
• to base itself on another class
• both allow the child to access
• the parent's capabilities
• note: inheritance != subtyping
• though often inheritance agrees with subtyping

Polymorphism

• allows a routine (function, method, constructor...)
• to use variables of different types
• at different times
• there are three kinds of polymorphism
  • ad hoc polymorphism
  • parameteric polymorphism
  • subtype polymorphism

Encapsulation

• allows an object (or a closure)
• to restrict outside access
• to some of its components
• and to bundle data with the routines
• that operate on that data

Abstraction (in an OO context)

• allows us to define objects which can...
• perform work,
• report on and change their state, and
• communicate with other objects

Abstraction enables encapsulation, polymorphism, and inheritance.