On Sat, 02 Aug 2008 17:45:03 +0200, Stefan Sobernig wrote:
Dear Squeakers,
(sorry for cross-posting; already posted to comp.lang.smalltalk)
For a piece of research I am currently working on, I have been reviewing the arsenal of publications on the genealogy of Smalltalk(s) for some hints on the origin of the Smalltalk-specific "subclass responsibility" approach, i.e. the Smalltalk dialect for "abstract object-classes", roughly speaking.
Interesting question (origin) indeed :)
I am particularly interested in references to design decisions. It would be particularly enlightening to know whether the Xerox crew was aware of the "virtual quantity" feature introduced in Simula-67 and their perception (beyond the mere difference with respect to type checking). I do have thoroughly studied "original" Smalltalk-related contributions, far beyond the Blue Book, but could not find explicit references beyond the mere fact that this is the Smalltalk way of doing it; but why?
Note that I am well aware of more recent discussions on that very matter, especially in your community on the semantic consistency of subclassResponsibility:
http://wiki.squeak.org/squeak/472
I am also aware of other language families that approach the idea of deferred-required implementation by means of a /placebo/ (what I would call it as a strategy).
Over at comp.lang.smalltalk, I was given as part of a more thorough answer:
Because we also need a way to respond for the general case of a message received that is not understood.
So, abstract super-classes are considered a special case deriving from a more general issue.
What I always liked are the paragraphs between "Inside every large program there is a small program trying to get out. ?C.A.R. HOARE" and "In class-based object-oriented systems, partial implementation is usually supported in the form of abstract classes." in the paper linked below.
What I mean is the emphasis on partial, incomplete implementation, made possible by late binding, a valuable tool for incremental development and maintenance.
Is anybody aware of some nuggets out there? I would be grateful for any hint + your thoughts when looking at your languages' history ...
Perhaps there are some nuggets in the paper from which the above was cited,
- http://portal.acm.org/citation.cfm?id=243439.243441
/Klaus
Best, //stefan