Object Oriented Programming

From APIDesign

This is my personal take on OOP. In case you are searching for objective view, then rather see official wikipedia's explanation.

Revolutionary view

Let me point you to an essay explaining OOP in completely revolutionary view. I especially like statements like:

• Typical object oriented program relies on functions more than many functional programs.
• λ-calculus was the first OOP language

Excellent explanation of the differences between OOP approach and the functional one can be summarized into:

• In classical OOP one only knows own identity. Identity (and implementation) of others can be inspected only by calling their methods (sending them messages)
• In functional world (when using algebraic types) the person that defines a type can inspect internals of all instances of the same type

The above characteristic of OOP leads to an interesting conclussion: OOP needs tail calls!

Last but not least the essay mentions the expression problem which I also analysed in TheAPIBook's chapter 18: Extensible Visitor Pattern Case Study.

History

OOP is no longer what it used to be. Somehow the original great visions diluted and instead we have class/object/inheritance as present in Java and other OOP languages of these days. The daily experience we have with these languages is so strong, so defining that we sometimes tend to forget that the roots of OOP used to be driven by visions and not technical concepts.

I was reminded about that recently when I read DCI introduction paper at artima website. Just few quotes:

Object oriented programming grew out as vision of the computer

as an extension of the human mind.

Wow! Really? Makes sense, but this is a piece of wisdom lost for a long time, am I right? Even when I learned about OOP I heard more the explanation describing the methodology as inspired by nature. The inheritance was the most natural way to define base class Mammal and subclasses Cat and Dog.

Our brain can definitely capture more complex concepts than the mammal example, so maybe, if we want to stick with the old definition, the meaning of OOP shall be expanded. Definitely beyond the expressive capabilities of C++ and Java.

MVC's goal was to provide the illusion of a direct connection

from the end user brain to the computer "brain"

a large method that represented an entire algorithm was believed to

not be a "pure" object-oriented design

This use of inheritance crept out of the world of programming

language into the vernacular of design