Re: Why Ada is not the Commercial Lang of Choice

[Ken Garlington <Kennie.E.Garlington@lmco.com>]

Robert Dewar wrote:
> 
> Keith said
> 
> <<GNAT follows this advice (the full type is modular, but that doesn't
> make literals available).  ObjectAda makes System.Address an access
> type.
> >>
> 
> That follows an old custom in Alsys compilers, where Address has always
> been an access type. What I do not like about this choice is that it means
> that the compiler always wants to initialize address values to the null
> pointer. This default initialization seems appropriate for access types,
> but I usually find it to be unwelcome junk overhead for addresses.
> 
> The modular representation seems more natural for modern machines.
> Historically one of the reasons for the Alsys choice was that the modular
> choice is NOT a good choice for the old junk segmented 286 architecture,
> and indeed if we still had to fight that machine, I would probably follow
> the access type decision, since it is indeed more portable in this sense.
> 
> (yes, yes, I know, the 32-bit x86 architecture still has segmentation, for
> gruesome details, see my book on Microprocessors - when Hennessey reviewed
> this section of the book, he wrote a large note asking "does anyone use
> this nonsense?" -- the answer to his question is pretty much no :-)

Of course, some of us still use 16-bit machines with segmentation (e.g.
MIL-STD-1750), but since by and large you can't get Ada 95 on such
machines,
it doesn't cause problems for Ada vendors.

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