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From: mab@dst17.wdl.loral.com (Mark A Biggar)
Subject: Re: Valid Attribute and Unchecked Conversion
Date: 1996/10/07
Message-ID: <53b658$c71@wdl1.wdl.lmco.com>#1/1
X-Deja-AN: 187330629
references: <3252ED6B.1B74@lmco.com> <53151i$ddd@newsbf02.news.aol.com>
 <32550731.167EB0E7@swl.msd.ray.com>
organization: Loral Western Development Labs
newsgroups: comp.lang.ada
Date: 1996-10-07T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <32550731.167EB0E7@swl.msd.ray.com> Karl Cooper {46901} <ktc@swl.msd.ray.com> writes:
>John Herro wrote:
>> I could be wrong, but I thought that Unchecked_Conversion is erroneous in
>> _any_ case.  I heard that the first validated Ada compiler, Ada/Ed, took
>> advantage of that fact and generated code to raise Program_Error wherever
>> the program tried to make use of Unchecked_Conversion.
>> Is this true, and if so, has any of it changed with Ada 95 and the new
>> 'Valid attribute?
>No, see the Ada83 reference manual 13.10, and the Ada95 reference
>manual 13.9 and 13.9.1.  Unchecked_Conversion leads to erroneous
>behavior in some cases, but not in others.  In my opinion, the
>Ada95 reference manual is clearer when describing the safe uses
>of Unchecked_Conversion.

Why was the Unchecked_Conversion of an invalid scalar made erroneous in LM 95 
instead of a bounded error like the coresponding uninitialized variable case?

--
Mark Biggar
mab@wdl.lmco.com