Re: advice on package design

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

On 17 Mar 2005 14:10:11 -0500, Robert A Duff wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> On 17 Mar 2005 09:04:26 -0500, Robert A Duff wrote:
>> 
>>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>> 
>>>> I agree with the idea, but I think that hiding should appear in a
>>>> declarative part. Less probably it should also qualify the thing being
>>>> hidden (like renames does):
>>> 
>>> I don't believe in declarative parts.  I think declare/begin/end
>>> should not be required just because I want to declare a constant
>>> or something.
>> 
>> Disagree. I don't like the idea of something changing its meaning within
>> the same scope, even if that is non-existing -> exiting. I have to tolerate
>> this in a declarative region because probably there is no better way to do
>> it. But I don't want to let it leak out of the quarantine zone.
> 
> I don't understand what you mean about "changing meaning".
> I just want to be able to write things like:
> 
>     for I in A'Range loop

Until here --> This_Component = nothing

>         This_Component: constant T := A(I);

Below --> This_Component = constant T

>         ... several uses of This_Component
>     end loop;
> 
> without adding three extra (useless) lines of code.
> And we agreed that if there's another thing called This_Component,
> this This_Component should not hide that This_Component.

Maybe it is a matter of taste, but it is one of things in C++ which I hate
the most. It is very difficult (to me) to understand a program with mixed
declarations and statements.

If you care about extra lines, then I'd propose:

   for I in A'Range -- All declarations be between for...loop
      This_Component: constant T := A(I);
   loop
      ... several uses of This_Component
   end loop;
 
> The "hide" command I proposed is of dubious value, but if it were
> allowed, I wouldn't mind restricting it to whole procedures
> or something.  Or not.  But either way, I don't like the separation
> of "declarations" and "statements".

I like the separation very much.

But let's consider getting rid of declarations. Wouldn't it be fake anyway?
You know that better than me, but I suppose the compiler will need to move
everything to the beginning of the closest scope. Otherwise:

   if Halt(x) then
     declare A;
   end if;
   Foo (A); -- Would it be legal?

   T := (1, 2, 4, declare X := 9, others => declare Y := 10);
      -- What would be this? How many Y's could be here?

So I see no advantage in this.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de