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From: ncohen@watson.ibm.com (Norman H. Cohen)
Subject: Re: Ada 95 case statement incompatibility?
Date: 1996/08/28
Message-ID: <5007k4$164a@watnews1.watson.ibm.com>#1/1
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distribution: world
references: <4vv4bs$hb8@erlang.praxis.co.uk> <4vvmra$k3t@linus.mitre.org>
organization: IBM T.J. Watson Research Center
reply-to: ncohen@watson.ibm.com
newsgroups: comp.lang.ada
Date: 1996-08-28T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <4vvmra$k3t@linus.mitre.org>, mfb@mbunix.mitre.org
(Michael F Brenner) writes: 

|> Another difference between 83 and 95 that was not documented is the
|> later rule that generics instantiated with signed numbers are
|> incompatible with generics instantiated with unsigned numbers.

But there were no unsigned types in the Ada-83 standard!  It is true that
some implementations provided implementation-defined (signed) integer
types whose operators were redefined to behave in roughly the same manner
as Ada-95 modular types.  However, since these types were
implementation-defined, an Ada-83 program using them was not portable
even to other Ada-83 compilers.  The fact that they may not be portable
to some Ada-95 compilers either is neither a surprise nor an
incompatiblity between the Ada-83 and Ada-95 standards!

There is nothing in Ada-95 to prevent vendors who provided these signed
types with modular behavior in their Ada-83 compilers from also providing
them in their Ada-95 compilers, in addition to the modular types required
by the Ada-95 standard.  Such types are redundant in the presence of
Ada-95 modular types, but provide a path for customers to migrate their
legacy Ada-83 code to Ada 95.

--
Norman H. Cohen    ncohen@watson.ibm.com