Re: Y2K Issues

[dewar@gnat.com]

In article <m3vhl224uy.fsf@mheaney.ni.net>,
  Matthew Heaney <matthew_heaney@acm.org> wrote:
> dewar@gnat.com writes:
>
> > P.S. Why don't we want customers adding grandchildren of Ada -- simple,
they
> > would potentially depend on internal private parts of the implementation of
> > these packages which we feel free to change without notice at any time!
>
> But isn't that the whole point adding the (grand)child - to get at the
> underlying representation of predefined types?
>
> If I add a child to Ada.Calendar, and the vendor changes the internal
> details of that package, then it's my problem!


If you are a manager, and one of your (incompetent) programmers introduces
dependencies on internal data structures of the compiler, which change without
warning with a new version of the compiler, so that your compiler no longer
works, who do you blame? Very often it is the vendor who gets the blame for
introducing incompatible changes. Yes, of course you can point out from a
legal point of view that it was the customer's fault, but that does not help
much. After all, when Intel produced the 80188 and stole one of the "reserved"
interrupts that was (mis)used by DOS, it is true that Intel was in the right,
but the bottom line was that the PC Junior, and other DOS based machines,
were not interested in this chip as a result.

We obviously can't stop anyone changing the compiler if they want to, and
introducing problems of this type, but we do like to make it clear to a
user that they are taking a potentially serious step in accessing internals
of the implementation, in terms of future compatibility. That is why we have
the -gnatg switch, which is to be used ONLY by GNAT implementors. Of course
users are free to use this switch (which among many other somewhat peculiar
things, allows you to add grandchildren to Ada -- if you follow the strict
style rules that are required). But as far as we are concerned, from an
official point of view, users should not use -gnatg.

By using a special switch, rather than casually allowing grandchildren of
Ada to be compiled and recompiled, we point out to the user that this is
non-standard Ada that may be incompatible with future compiler versions.

Robert Dewar
Ada Core Technologies

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