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Date: 6 Apr 93 16:46:42 GMT
From: mcsun!julienas!newsserver!geant!bruniau@uunet.uu.net  (Christophe Bruniau
)
Subject: Re: Classes vs Tagged Types - Terminology
Message-ID: <1993Apr6.164642.9487@cenatls.cena.dgac.fr>
List-Id: <comp.lang.ada>

In article <1993Apr5.155419.8598@evb.com>, jgg@evb.com (John Goodsen) writes:
|> In <1993Mar25.155650.16244@inmet.camb.inmet.com> 
|> stt@spock.camb.inmet.com (Tucker Taft) writes:
|> 
|> >
|> >In Ada 9X, it is only class-wide types (named "T'Class") that provide
|> >subclass matching.
|> >                      ^^^^^^^^^^^^^^^^^
|>                        Didn't you mean "tagged types" :-)
|> 
|> Can we take this as an indicator that you are about ready to
|> abondon the "tagged type" terminology and adopt the more
|> appropriate "class type" terminology?  It seems that even
|> members of the 9X project are shying away from using "tagged
|> type" these days, so why don't just finish the scenario and
|> adopt the "class type" syntax and terminology ...
|> 
|> fingers crossed...
|> 

Does anyone know the original reason why "tagged type" was introduced,
 instead of something like "class type" ?

I think that a terminology like "class type" would make explanations like
 the one below more straightforward.
This could make Ada-9X more "sexy", for those who don't see immediately
its advantages :-)

>Given a tagged type T and two derived types T1 and T2, you get the
>following:  T1'class and T2'class are subclasses of T'class.
>Any object belonging to the specific type T1 is thus an instance of
>T1'class and of T'class.  Same for T2, mutatis mutandis.  Any object
>belonging to the specific type T is an instance of T'class (but not of
>T1'class, of course). Thus:
>	X : T;  -- instance of T'class
>	Y : T1; -- instance of T1'class and T'class
>	Z : T2; -- instance of T2'class and T'class


Christophe BRUNIAU     bruniau@cenatls.cena.dgac.fr