Re: Discriminants of tagged types

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 27 Paź, 23:23, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:

> Funny, I usually do the exact opposite.
>
> I usually represent these things with untagged limited types.  Why would
> these objects need to be tagged?

In my systems these are tagged to allow different implementations. A
database connection will be implemented differently for Oracle and for
PostgreSQL, although they may share a common interface.

Streams are good examples from the Ada standard library.

> Conversely, my tagged types do not
> necessarily (or usually, for that matter) represent resources; they
> represent data with behavior or GUI widgets.

GUI widgets are in the same category for me. They represent something
from outside of the program - copying windows objects is meaningless,
so it is safer to forbid copying whatsoever by making these types
limited.

I did not have to use types that are polymorphic and naturally
copyable.

--
Maciej Sobczak * http://www.inspirel.com