Re: Classes vs Tagged Types - Terminology

[nebbe@lglsun.epfl.ch (Robb Nebbe)]

In article <EMERY.93Mar24191542@dr_no.mitre.org>, emery@dr_no.mitre.org (David Emery) writes:
: >Tagged types will probably be a peculiarity of Ada (although certainly
: >justified in Ada's case) and I don't think we will be seeing other
: >languages with tagged types.
: >
: > Robb
: 
: Modula-3, if I'm not mistaken, uses the same idea as Ada 9X...
: 				dave

Modula-3 provides what they call object types but are really just classes
in disguise. Modula-3 has adopted a whole new vocabulary but doesn't do
anything fundamentally different from all the other "OO" languages such
as Smalltalk, Eiffel, Simula, C++, and Objective C. The purpose of the
Modula-3 vocabulary seems to be to give the appearance that object types
(classes) are well integrated into the type system. This just serves to
cover up the fact that Modula-3 is a hybrid language.

This is to be contrasted with Ada 9X, where the approach is fundamentally different and the syntax reflects this difference.  Ada 9X fully integrates
the new OO features with the old OO features. This approach seems to provide
quite a few advantages and will certainly be a plus for Ada.

The language that comes the closest conceptually to the approach used
in Ada 9X is Oberon. Ada 9X is clearly more powerful, but it seems to me
that in some cases the solution chosen in Oberon is more appropriate
than the solution chosen in Ada 9X; The Ada 9X solution looks a lot like
Eiffel in some ways and I'm not sure if it is appropriate or not. Only time
will tell.

Robb