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Date: 23 Oct 92 20:43:05 GMT
From: seas.gwu.edu!mfeldman@uunet.uu.net  (Michael Feldman)
Subject: Re: Uninitialized subtype variables
Message-ID: <1992Oct23.204305.27291@seas.gwu.edu>
List-Id: <comp.lang.ada>

In article <1992Oct22.134607.17193@inmet.camb.inmet.com> stt@spock.camb.inmet.c
om (Tucker Taft) writes:

[good stuff deleted]
>
>It's a bag of worms, but we are still trying to do something about it ;-).
>Uninitialized scalar variables are one of the few "holes" left in the
>Ada safety net, and it would be nice to somehow narrow the hole a bit.
>Of course, some kind of "pragma SUPPRESS" should be provided to rip
>it open again on user request, but we would like the RM to specify
>essentially "safe" semantics as the default, presuming it can
>be done without unduly complicating the semantics nor significantly 
>hurting code quality.

At the very least, allow some sort of programmer-specified initialization
for all types, including scalar types. I know there are some tricky
problems with this, but inituitively there ought to be a way to make
it work (maybe restrict initializations of this kind to be static).

In Ada83, the only types for which I can supply initializers are record
types; wrapping a record around a scalar type just so I can initialize
it is rather too kludgy for my taste. Better that I can say:

  SUBTYPE Little IS Integer RANGE -10..10 := -10;

or even

  TYPE Vector IS ARRAY (Integer RANGE <>) OF Float := (OTHERS => 0.0);

Even with this unconstrained type, surely the compiler can defer the
initialization till object allocation time.

At one point this was to be in Ada-9X but was eliminated at some
stage. 

We've been around this loop before, and I know there are some sticky
situations, but as I recall they were rather pathological, so perhaps
the rules could be written to end-run them. From a teachability point
of view, this uniformity would be a big winner.

Comments, Tucker?

Mike Feldman
------------------------------------------------------------------------
Michael B. Feldman
co-chair, SIGAda Education Committee

Professor, Dept. of Electrical Engineering and Computer Science
School of Engineering and Applied Science
The George Washington University
Washington, DC 20052 USA
(202) 994-5253 (voice)
(202) 994-5296 (fax)
mfeldman@seas.gwu.edu (Internet)

"Americans wants the fruits of patience -- and they want them now."
------------------------------------------------------------------------