Re: "out" or "access"

[Robert A Duff <bobduff@world.std.com>]

Matthew Heaney <matthew_heaney@acm.org> writes:

> The RM also recommends that implementations "deliver a useful result"
> when you take the O'Address of a by-reference type (tagged types,
> limited types) passed as a subprogram parameter.  That's why
> Sys.Addr_To_Acc_Conv can be used to work around this problem.

I don't understand why you want to use 'Address at all.
My earlier suggestion was to use 'Unchecked_Access.
It has the same problem with possible dangling references,
but at least it doesn't throw type checking completely out
the window, as 'Address does.

>    type My_Iterator is 
>       new Iterator with record
>          Stack : Conv.Object_Pointer;
                   ^^^^^^^^^^^^^^^^^^^
Say My_Stack_Ptr, which is declared "access constant My_Stack", and then...
>          Index : <some index type>;
>       end record;
> 
>    function Initialize (S : My_Stack) return Iterator'Class is
>    begin
>       return My_Iterator'(To_Pointer (S'Address), S.Top);

       return My_Iterator'(S'Unchecked_Access, S.Top);

>    end;

By the way, have you considered making the iterators limited,
and initializing them with a discriminant that points to the
Stack (or whatever is being iterated)?

- Bob
-- 
Change robert to bob to get my real email address.  Sorry.