Re: Limited_Controlled types as 'out' arguments

[Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>]

On Thu, 31 Jul 2003 12:19:17 +0000 (UTC), Lutz Donnerhacke
<lutz@iks-jena.de> wrote:

>* Dmitry A Kazakov wrote:
>> On Thu, 31 Jul 2003 10:54:44 +0000 (UTC), Lutz Donnerhacke
>>>   procedure Set(o1, o2 : out Test; i : Test) is
>>>   begin
>>>      Debug("Setting from", i.a);
>>>      Debug("Setting o1  ", o1.a);
>>>      Debug("Setting o2  ", o2.a);
>>>      Finalize(o1);
>>>      Finalize(o2);
>>>      
>>>      o1.a := new Character'(global);
>>>      Debug("Setting to1 ", o1.a);
>>>      global := Character'Succ(global);
>>>
>>>      o2.a := new Character'(i.a.all);
>>>      Debug("Setting to2 ", o2.a);
>>>   end Set;
>> 
>> Sort of, if you are calling Finalize from a normal subprogram! (:-))
>> As for error, you call Set (a, a, b); which finalizes a twice! It is a
>> language design fault that a destructor can be called explicitly. Your
>> example shows why.
>
>Changing the "Finalize" calls to "Free" causes the same effect.
>So the main point is: How to manage resources correctly?

What do you mean? Aliasing problem or assignment of limited types?
Anyway what should not be confused is that assignment, copy
constructor, copy procedure, all are very different things.

>   procedure Set(o1, o2 : out Test; i : Test) is
>   begin
>      Debug("Setting from", i.a);
>      if o1'Address /= o2'Address then
>         Debug("Setting o1  ", o1.a);
>         Free(o1.a);
>
>         o1.a := new Character'(global);
>         Debug("Setting to1 ", o1.a);
>         global := Character'Succ(global);
>      end if;
>
>      Debug("Setting o2  ", o2.a);
>      Free(o2.a);
>      o2.a := new Character'(i.a.all);
>      Debug("Setting to2 ", o2.a);
>   end Set;
>
>GNA!

This should work.

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de