Posts Tagged ‘language design’

Nicklaus Wirth on object-oriented programming

From Professor Nicklaus Wirth, the father of Pascal, the Modulas, and Oberon on OOP,

“Many people tend to look at programming styles and languages like religions: if you belong to one, you cannot belong to others. But this analogy is another fallacy. It is maintained for commercial reasons only. Object-oriented programming (OOP) solidly rests on the principles and concepts of traditional procedural programming (PP). OOP has not added a single novel concept, but it emphasizes two concepts much more strongly that was done with procedural programming. The fist such concept is that of the procedure bound to a composite variable called object. (The binding of the procedure is the justification for it being called a method). The means for this binding is the procedure variable (or record field), available in languages since the mid 1970s. The second concept is that of constructing a new data type (called subclass) by extending a given type (the superclass).

It is worthwhile to note that along with the OOP paradigm came an entirely new terminology with the purpose of mystifying the roots of OOP. Thus, whereas you used to be able to activate a procedure by calling it, one now sends a message to the method. A new type is no longer built by extending a given type, but by defining a subclass which inherits its superclass. An interesting phenomenon is that many people learned for the first time about the important notions of data type, of encapsulation, and (perhaps) of information hiding when introduced to OOP. This alone would have made the introduction to OOP worthwhile, even if one didn’t actually make use of its essence later on.

Nevertheless, I consider OOP as an aspect of programming in the large; that is, as an aspect that logically follows programming in the small and requires sound knowledge of procedural programming. Static modularization is the first step towards OOP. It is much easier to understand and master than full OOP, it’s sufficient in most cases for writing good software, and is sadly neglected in most common languages (with the exception of Ada).

In a way, OOP falls short of its promises. Our ultimate goal is extensible programming (EP). By this, we mean the construction of hierarchies of modules, each module adding new functionality to the system. EP implies that the addition of a module is possible without any change in the existing modules. They need not even be recompiled. New modules not only add new procedures, but – more importantly – also new (extended) data types. We have demonstrated the practicality and economy of this approach with the design of the Oberon System.”

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