Re: Type safety on wikipedia

[Martin Krischik <krischik@users.sourceforge.net>]

Jan Andres wrote:

> On 2006-01-27, Martin Krischik <krischik@users.sourceforge.net> wrote:
>> with Ada.Text_Io;
>>
>> procedure Access_Test is
>>     type Int_Access is access Integer;
>>     procedure Deallocate is new Unchecked_Deallocation ....
>>
>>    P : Int_Access := new Integer;
>>    Q : Int_Access := P;
>> begin
>>     Deallocate (P);
>>     Ada.Text_Io.Put_Line(Integer'Image(Q.All));
>>  end Access_Test;
> 
> Hmm, but aren't all the restrictions on the scope of access values
> actually there in order to guarantee type safety, as long as no unsafe
> constructs like 'Unchecked_Access are used? Or is
> Unchecked_Deallocation itself considered to be such an unsafe construct?
> If so, is there any "safe" alternative in Ada that we can use if we
> don't have GC?

No, there is no save alternative. There is a talk page where the authors of
the page discuss the page content and how to improve.

From there it becomes more and more clear that strictly type save language
might only be a special purpose language and that general purpose languages
can't be type save. A bit like original Pascal.

If you look at the page now: There is no list of type save languages - there
is a list of almost type save languages and there weak spots. Even
Standart-ML has a weak spot: interfacing with other languages.

Ok, there is SPARK. But for once SPARK is special purpose and hey, does
SPARK not allow interfacing with other non-type-save languages?

> Of course you could simply avoid such constructs as quoted above but
> the downside is that the language will not actually enforce this.

Indeed. For me this discussion means that I will renew my effort on garbage
collection in Ada. AdaCL was the next on the list for the gnuada
distribution anyway - now that ASIS has been added.

Martin
-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com