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From: "per" <commander@death-star.com>
Newsgroups: comp.lang.ada
Subject: Re: OO problem: Performing actions on messages (very long, sorry)
Date: 10 Jan 2005 00:42:44 -0800
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Date: 2005-01-10T00:42:44-08:00
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>How do you plan to maintain data consistency of a message if the user
may
>arbitrarily override its fields? I would try to do it more OO. To
think

Well, that's the user's problem. Or rather, that's the point, sort of.
See, this is a test equipment and shall enable modification of messages
in "any" way in order to test how the test object (a computer) reacts.

>about what can be done with a message. And consider action as an
>implementation detail of a concrete type of messages. Then actions
could
>vanish. (Just a guess, I still can't tolerate both messages and
actions in
>one bottle. (:-))
>
>> Can an action, eg Override_A, exist without an M1 instance to
"point"
>> at?
>
>It cannot, this is the whole idea of access discriminants. They are
never
>null and cannot be changed. Otherwise one should use access types
>(pointers).
>
>> Action has a different life-cycle than Message.
>
>That's no problem as long as its life in Message's one. For exampe:
>
>declare
>  M : aliased M1;
>begin
>  ...
>  declare
>     A : Override_A (M'Access);
>  begin
>     ... -- The scope of the action A is nested
>  end;
>  ...
>end;

How would you create a schedule of actions before any messages exist?
(Schedule = Plan of what actions should be taken to what type of
messages and when, created *before* any message instances exist)