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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Ensuring postconditions in the face of exceptions
Date: Mon, 15 Mar 2010 10:33:12 -0700 (PDT)
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Date: 2010-03-15T10:33:12-07:00
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Robert A Duff wrote on comp.lang.ada:
> Ludovic Brenta <ludo...@ludovic-brenta.org> writes:
> > No, Dirty is not a property of the object; the type T is used in
> > several places, only some of which (a one-line cache, essentially) has
> > a Dirty property.
>
> OK, then Dirty is a property of the cache. =A0So how about:
>
> =A0 =A0 type Cache is limited
> =A0 =A0 =A0 =A0 record
> =A0 =A0 =A0 =A0 =A0 =A0 X : T;
> =A0 =A0 =A0 =A0 =A0 =A0 Dirty : Boolean :=3D True;
> =A0 =A0 =A0 =A0 end record;
> =A0 =A0 type Cache_Ref is access all Cache;
>
> and pass a parameter of type Cache_Ref? =A0(Or perhaps
> X could be an access type, and point to the T object.)
>
> You need to pass some sort of pointer, explicitly or implicitly,
> because when you raise an exception, the copy-back is skipped.
> You said that relying on limitedness to force pass-by-referrence
> is confusing -- I agree. =A0So pass an explicit pointer.
>
> I recommend a named access type, because anonymous access parameters
> have dynamic accessibility, which is a tripping hazard, and is
> less efficient.

Yes, that's the solution I have, currently, i.e. (5); except that the
Cache type already existed before, has other unrelated components and
is not limited.

--
Ludovic Brenta.