Re: private type discriminants ignored?

["Patrick D. Rogers" <p_rogers@hso.link.com>]

Samuel T. Harris wrote:
> 
> Robert A Duff wrote:
> >
> > In article <rz84szje1ol.fsf@cs.williams.edu>,
> > Jay Sachs  <sachs@cs.williams.edu> wrote:
> > >       type Stack(Size : Integer := 100) is private;
> >
> > >...  What is the reason that the default initialization
> > >seems to be ignored in the discriminant for the private type?
> >
> > The default isn't being ignored; Size is being correctly initialized to
> > 100.  However, the mere presence of a default means that the
> > discriminant can change.  That's confusing, and is a language design
> > flaw, IMHO.  There should have been a separate keyword or some other
> > separate syntax to mean "the discrim might change".  But as it is in
> > Ada, an unconstrained variable of type Stack can later have a discrim of
> > Integer'Last, even though it defaults initially to 100.  And many
> > compilers take the (quite reasonable) attitude that implicit heap
> > allocation is evil, so they allocate the maximum possible size for these
> > things.  And in this case, that's enormous, and will typically raise
> > Storage_Error; hence the warning.
> 
> Not entirely accurate. The mere presense of the default value does
> not mean the discriminant can change. It depends on how objects
> are declared.


Sam,

Since we are in pedantic mode, :) Bob said "... unconstrained variable
...", so he is indeed entirely accurate.

:) 


--pat

Patrick Rogers