From: sommar@enea.se (Erland Sommarskog)
Subject: Re: Overloading of ":="
Date: 26 Dec 88 13:07:14 GMT [thread overview]
Message-ID: <4193@enea.se> (raw)
Bill Wolfe (billwolf@hubcap.clemson.edu) writes:
>From article <4189@enea.se>, by sommar@enea.se (Erland Sommarskog):
>> [Mats Weber and Erland Sommarskog rehash the argument about
>> assignment procedures having an "in out" parameter for the destination]
>>
>> Now, WHY, is A of mode "in out" in the Assign procedure? If we had
>> "out" only, nothing "erroneous" could occur.
>
> Because the ASSIGN procedure needs to be able to DESTROY the old
> value; DESTROY procedures must read objects during the process
> of destroying them. Please review the recent discussion rather
> than recreating it, unless there are new issues to be considered.
Talk about rehash. We all know, except Bill of course, that the memory-
management problem is best handled with garbage collection.
As for the answer to the question above, the answer is simply that
Generic
Data_type is limited private;
With procedure Assign(A : out Data_type; B : in Data_type);
Package...
is illegal. Parameters of a limited type may not be in "out" mode.
This means, as Mats pointed out, that to use this package for
type without a default value, like standard.integer, the user have to
do something erroneous. I, in my turn, pointed out that this was not
a problem in practice except for constrained types, and that this
case also easily was handled with a "supress" pragma.
Please read more carefully before you flame. We didn't talk about
memory management. We didn't even talk about access types.--
Erland Sommarskog
ENEA Data, Stockholm This signature is not to be quoted.
sommar@enea.se
next reply other threads:[~1988-12-26 13:07 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
1988-12-26 13:07 Erland Sommarskog [this message]
1988-12-28 5:46 ` Overloading of ":=", ADT survivability William Thomas Wolfe,2847,
-- strict thread matches above, loose matches on Subject: below --
1988-12-24 22:02 Overloading of ":=" Erland Sommarskog
1988-12-25 19:27 ` William Thomas Wolfe,2847,
1988-12-20 13:05 Mats Weber
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