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From: Kilgallen@SpamCop.net (Larry Kilgallen)
Newsgroups: comp.lang.ada
Subject: Re: Attributes 'Version and 'Body_Version
Date: 7 Nov 2001 13:54:20 -0600
Organization: LJK Software
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In article <9sboee$42f$1@nh.pace.co.uk>, "Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org> writes:

> It might not hurt for Ada0x to insist that Something'Version and
> Something'Body_Version yield a string that is increasing in sort order with
> each change. That at least would let you do "<" and ">" comparisons and know
> you are still portable.

At first glance this sounds like VMS shareable image matching
controls that are done manually, where numeric comparisons are
possible.  But the Ada feature seems to require something like
VMS shareable image matching controls that are done automatically,
and necessarily allows only equality comparisons.  I will not be
available to code the fully automatic relationship-comparing
version until I finish the required preliminary work on the
DWIM subprogram :-).

=======

Consider:

Something'*Version is required by the standard to change anytime
there is a change in a compilation unit referred to by Something.

So presume one changes both SubOne and SubTwo and then recompiles
Something.  Say the compiler takes the next logical sort ordered
value.

Then what happens if one rolls back SubTwo to what it used to be,
but retains the changed version of SubOne ?  The result we have is
_logically_ between the original and the first modification, but that might
be hard to achieve in the sort order.  Or what if we make _another_
version that has the original version of SubOne but retains the
change to SubTwo ?  How does the value of _that_ string relate
to the value of the one whose context is vice versa ?