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Newsgroups: comp.lang.ada
Date: Wed, 25 Jan 2017 00:38:52 -0800 (PST)
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Subject: Question on type invariants
From: reinkor <reinkor@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:33154
Date: 2017-01-25T00:38:52-08:00
List-Id: <comp.lang.ada>

This question may be a bit imprecise:

Assume a complex object A (for example a set of records stored in a Contain=
er or file). Let S (for example an array of records) represent a summary of=
 A (derived=20
from A).

I want to update S (call "Update_S") in an economical way. S may not be upd=
ated immediately each time A changes. And I would prefer not to update too =
much when S is up-to-date anyway (i.e. avoid redundant updating). I also wa=
nt to keep things simple and avoid to combine updating S in any smart way w=
hen I change A (I may not have full control over the modifications of A any=
way). The main thing is that S in "fresh"/updated when I use it (not necess=
ary when A changes).

In principle I could mark A and S with a "last-modified-time-flag" so I can=
 update S when I find it necessary. This has similarities to unix "make". B=
ad idea?

I can program the whole thing and keep the concepts in my head, but is it a=
 natural "Ada way" to secure that S is up-to-date when used? Is "type invar=
iants" of any help?

reinert