Re: use of attribute Pos

["Pat Rogers" <progers@NOclasswideSPAM.com>]

"Philippe Torres" <ptorres@laas.fr> wrote in message
news:39E5DE79.F61616EC@laas.fr...
> Pat Rogers wrote:
> >
> > "Philippe Torres" <ptorres@laas.fr> wrote in message
> > > But now, i wonder why Alejandro's solution
> > > ----
> > > type Upper is new Character range 'A'..'Z' ;
> > > begin
> > > Put(Upper'Pos('A')) ;
> > > ---
> > > still manages to output 65 and not 0.
> > >
> > > Since a different type is introduced, how does Pos still refer
to
> > > Character ?
> > > Should not 'new' have broken all "links" between the types
Character
> > and
> > > Upper ?
> >
> > Now things get a little bit more involved.  :-)   The terminology
> > invariably confuses people, so I won't be precise in that regard.
> > Let's just say that what you really have here is a subtype of a
type
> > derived from Character.  Since it has a distinct name (Upper) it
is a
> > distinct type, but it is still a constraint on Character.
> >
> > Hope that helps, as opposed to making it worse!  :-)
> >
>
> OK but to me it would have been more logical to have the attribute
Pos
> reflecting exactly the position of the element in the range of the
type
> which has been "ticked".
> Anyway thanks for your help but it's a bit misleading for a newbie
like
> me to guess which are the attributes "overloaded" by a subtype or a
> derived type and which are merely "inherited such as" from the base
> type.

Instead of

    type Upper is new Character range 'A'..'Z' ;

imagine you wrote it this way:

    type Anonymous is new Character;
    subtype Upper is Anonymous range 'A' .. 'Z';

That's effectively what you've got.   Anonymous'Pos('A') would be 65,
and thus so is Upper'Pos('A')

Better?

---
Patrick Rogers                      Consulting and Training in:
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