Re: [RFA] Add type support for Ada

Jim Blandy
2002-10-02T18:57:48Z

"Paul N. Hilfinger" <hilfingr@otisco.mckusick.com> writes:
> > It looks to me as if the string cleanup stuff is distinct from the
> > fixed instance stuff. These should be submitted as separate patches.
>
> They definitely are logically separate changes.
>
> > Is a `fixed instance' a feature of the language's type system itself?
> > That is, is it something that an Ada programmer actually knows about?
> > Or is it something used internally within GDB, or internally by some
> > implementations of Ada?
>
> It is not a language feature, but rather an optimization. The original
> problem was that STABS and also GDB's internal type representation
> was not adequate for representing "dynamic" Ada types---i.e., those that,
> unlike C types, have data-dependent sizes. The scheme we hit on (in
> retrospect perhaps not the best) was to encode a bunch of auxiliary
> information into our type names, and to introduce additional types
> carrying additional (encoded) information.
>
> When Ada evaluation routines discover that a quantity has an encoded
> type, they know to compute a conventional, fixed-sized GDB type based on the
> data, and to attach this type to the value they are producing.
>
> Unfortunately, the computations involved are expensive---involving type
> lookups in some cases---and we don't want to repeat them unnecessarily.
> Hence the flag.

Thanks for the explanation. Since this isn't a language feature, but
an implementation detail, the patch needs to add comments that explain
it in full detail. Something like the above, but with the exact Ada
terminology stuck in at the right places, would be a start.