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Path: utzoo!attcan!uunet!mcvax!enea!sommar
From: sommar@enea.se (Erland Sommarskog)
Newsgroups: comp.lang.ada
Subject: Re: Overloading of ":="
Message-ID: <4193@enea.se>
Date: 26 Dec 88 13:07:14 GMT
Organization: ENEA DATA AB, Sweden
List-Id: <comp.lang.ada>

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