7 - THE DREADED SUPER

Summary

This is a bit of work I am particularly proud of. I wrote a little workspace that got me a method list browser on all the methods in the image that use “super” (that in itself was fun). Then I went through them trying to categorize each one. I felt like a real scientist there for a minute- taking samples, making hypotheses, testing them in the “real world.” The result is a “theory of super,” which is much simpler than the language feature (and perhaps not coincidentally quite similar to the “inner” feature of Simula, from which super was derived).

What is it with this super thing, anyway? The pseudo-variable super is a curious wart on the otherwise unblemished Smalltalk language design. Ordinary messages are sufficient to capture composition, conditionals, and looping. The three components of structured programming thus become unified in Smalltalk. Yes, but.…

The exception is super. It means the same object as self, but when you send it a message the difference is revealed. When you send an ordinary message the class of the receiver of the message is examined for an implementation of that message. If one is not found the superclass is searched, then its superclass, and so on until a method is found. Super circumvents normal message lookup. When you send a message to super the search begins in the superclass of the class in which the executing method was found.