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From: dlindsle@afit.af.mil (David T. Lindsley)
Newsgroups: comp.lang.ada
Subject: What should this do?
Summary: Is this legal, or not?
Keywords: Variable-length strings constraint exception
Message-ID: <1991Jun28.193513.14271@afit.af.mil>
Date: 28 Jun 91 19:35:13 GMT
Organization: Air Force Institute of Technology
List-Id: <comp.lang.ada>


I have a question about dynamic strings.  I was looking at a package
on simtel20 that did the following:

             subtype INDEX is natural range 0..100;
             type DYN_STRING (SIZE : INDEX := 0) is private; 

--           private
--                 type DYN_STRING (size : index := 0) is
--                    record
--                        DATA : string (1..size);
--                    end record;

the second declaration had a note to the effect of "uncomment and use
this if you've got a VALIDATED compiler".

Now as far as I can tell, during elaboration, a declaration of the form

	S : DYN_STRING;

will result in the attempt to allocate an array constrained to (1..0),
which should raise an exception.  At least, that's what it does under
VAX Ada, but not on Verdix.  (Both generate warnings.)

It seems to me this has to be a bug in one of the compilers.  My question
is: whose?  Should this, or should it not, raise an exception?  (The
LRM references weren't any help.)

-- 
Dave Lindsley	#24601#			OPINIONS.  MINE.  (Nobody tells me
dlindsle@blackbird.afit.af.mil		  anything anyway, so I can't possibly 
    ?? lamroN eb yhW ??			  be anybody's mouthpiece...)