Re: Why constant components are not permitted ?

[David Sauvage <david.sauvage@adalabs.com>]

On 29 nov, 08:10, "Randy Brukardt" <ra...@rrsoftware.com> wrote:
> "Niklas Holsti" <niklas.hol...@tidorum.invalid> wrote in message
>
> news:9ja2aiFla6U1@mid.individual.net...
> ...
>
> > The original poster specified the constant value in the declaration of the
> > record *type*, not separately for each record *object*. This is what I do
> > not understand: what is the use of a value that is the same for all
> > objects in which it can appear?
>
> One such use is in interfacing when some components always have fixed
> values. For instance, most record types in Win32 have a Size component that
> is always the same for a particular type declaration. It would be nice to
> declare that as a constant (since it cannot change).
>
> But this need is so rare and unusual it hardly makes sense to add language
> support for it. The story would be different for a new from-scratch language
> design; the omission looks like a mistake in Ada and it surely would be more
> consistent to have it even if it is rarely used. But redoing the Standard
> and existing implementations needs a better reason than "more consistent but
> rarely used".
>
>                                  Randy.


Why use a constant attribute in a record ?

To expose my design intention in the code.

I will have a big tagged types hierarchy, and wanted to declare a read
only component in each root tagged types, so that when users will use
the framework and add child types, they will not been able to modify
this attribute.
I would not been able to do this using a primitive method as they
would be able to override it (think of the final keywork in Java to
prevent a method from being overridden).

Anyway, my question concern the rational of why this is not possible
in Ada, and I got some answers.

Thanks to all for your inputs.

Cheers,