Re: Ensuring postconditions in the face of exceptions

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Ludovic Brenta <ludovic@ludovic-brenta.org> writes:

> 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. �So how about:
>>
>> � � type Cache is limited
>> � � � � record
>> � � � � � � X : T;
>> � � � � � � Dirty : Boolean := True;
>> � � � � end record;
>> � � type Cache_Ref is access all Cache;
>>
>> and pass a parameter of type Cache_Ref? �(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. �So 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.

Right, but you said you didn't like it, because of the "other unrelated
components".  So the type I'm suggesting above is a different one
than the existing one -- I'm suggesting this new type would NOT
have the unrelated components.

I haven't seen your code, of course, so I could be talking
complete nonsense.  ;-)

- Bob