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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Ada 83 - avoiding unchecked conversions.
Date: 1996/12/26
Message-ID: <dewar.851609561@merv>#1/1
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references: <md5:8B831999BCF200C6E70994BDF6CC529F> <32AED68A.48BE@aisf.com>
 <32b03008.564464@netnews.worldnet.att.net> <58np72$9qp@news.nyu.edu>
 <32B6905F.FC4@tiac.net> <dewar.850929268@merv> <E2ooC4.FMy@thomsoft.com>
organization: New York University
newsgroups: comp.lang.ada
Date: 1996-12-26T00:00:00+00:00
List-Id: <comp.lang.ada>


Keity says

"I agree that the compiler needs to emit a shift for this case, but
it shouldn't generate a check that the result is within the declared
range of its subtype.  This makes it the programmer's responsibility to
guarantee that the result will be a valid value of the target subtype
(if possible, by using a target subtype that covers all possible bit
patterns), or to deal with it properly if it isn't."


Notice that the shouldn't here corresponds to implementation advice in the
RM, not to any requirement, so code that counts on there being no check
is potentially non-portable.