Object-oriented programming

OOP is a programming paradigm based on the concept of "objects", which may contain data, in the form of fields often known as attributes; and code in the form of procedures, often known as methods. We are aiming to group related data and functions.

  • Encapsulation: tie the data and the functions that are acting together in a class.
  • Composition
  • Delegation) is calling a routine "in another context", for instance calling a base class member function from an instance of a derived class.
  • Open recursion
  • Abstraction: providing only essential information to the outside world and hiding their background details, separation of interface and implementation.
  • Decoupling: removing dependencies on external computations/data.
  • Low coupling, high cohesion



Polymorphism means "many forms" and describes the ability of an operation to change behaviour according to its arguments.

Ad-hoc polymorphism

Function and operator overloading.

Writeln(Add(1, 2)); (* Prints "3" *)
Writeln(Add('Hello, ', 'World!')); (* Prints "Hello, World!" *)

Parametric polymorphism

Function does the same thing for different types: templates in C++.

Sub-typing (inheritance)

Class hierarchies, diamond inheritance.

Static and dynamic polymorphism

Polymorphism can be distinguished by when the implementation is selected: statically (at compile time) or dynamically (at run time, typically via a virtual function). This is known respectively as static dispatch and dynamic dispatch, and the corresponding forms of polymorphism are accordingly called static polymorphism and dynamic polymorphism.

Other considerations

OOP programming in C++ is not particularly elegant in some instances. And can be very nuanced and easy to introduce subtle bugs. Also, if you inherit from a class it might not be immediately clear what other stuff you have also inherited.


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