Microsoft Word OpenIssuesInOO. doc

Summary 

BETA has succeeded in unifying class, procedure/method, etc into the pattern concept.  We 

are more skeptical to the extent to which objects and classes have been unified in prototype-

based languages.  If a prototype-based language does not support class-based programming 

then it has not unified class and object. One may argue of course that it is not important to 

support class-based programming, but this is another discussion. 

The division between class-based and prototype-based languages is perhaps more 

blurred than it may appear: In BETA it has always been possible to describe so-called 

singular objects. A singular object is described directly, not as an instance of a class. This 

was motivated from a modeling as well as a technical point-of-view. In the real world you 

often encounter one-of-a-kind phenomena that you may not wish to model as an instance of 

a class. Technically it is inconvenient to invent a class name and an instance name for such 

single objects. A (singular) object in BETA can be used to generate a new object with a 

similar structure. It cannot be cloned, but such an operation could easily be added to the 

implementation. BETA does not support implicit delegation, but explicit delegation is 

possible, see e.g. Reference [MM92]. Finally BETA does not support operations for adding 

and removing attributes (slots in Self terminology). Such operations could be added to the 

language, but will in general require an incremental environment for handling type checking 

in order to be useful. 

Pattern variables in BETA make classes, procedures, etc., first class, which means that 

they can passed around as objects.  

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It would be desirable if class and object could be completely unified and still provide the 

style of class-based programming that has proven its usefulness for modeling as well as 

implementation. This unification should also  cover method and block.