Re: Classes vs Tagged Types - Terminology

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

In article <C4AGp4.1Fw@clw.cs.man.ac.uk>, chl@clw.cs.man.ac.uk (Charles Lindsey) writes:
: TYPE With INHERITANCE
: Example: Tagged Types in Ada 9x
: These are to enable "Object Oriented Programming" in PACKAGE-based
: languages. The concept seems good, and the (possible) advantages of
: PACKAGE-based systems over CLASS-based systems are retained. The term
: "Tagged Type" is used because values of such Types need to carry a Tag
: around at runtime. However, some complain that implementation details
: should not carry over into the syntax of High Level Languages, so maybe
: some other term is needed. I offer "Classified Type" for your
: consideration.
: 

We shouldn't leave Oberon out of this discussion since it is already
available and Ada 9X is still only a proposal. Oberon implements
inheritance for record types and Wirth even goes out of his way to
avoid mentioning the word "tag" when talking about the concepts in his
book. Oberon also rather neatly avoids the distributed overhead incurred
by Ada; objects with a specific type have no need for a tag and so the
only objects that have tags are record pointers which don't necessarily
always point to an object of the same specific type.

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.

: Charles H. Lindsey 

Robb Nebbe