Re: Bus error

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

On Fri, 29 Jun 2007 17:44:22 +0200, Georg Bauhaus wrote:

> Dmitry A. Kazakov wrote:
>> On Fri, 29 Jun 2007 11:35:28 +0200, Duncan Sands wrote:
>> 
>>> in Ada 95 you could do
>>>
>>> 	X : T renames Factory;
>> 
>> Yes, you're right. It should be illegal. Semantically it is same as
>>
>>    X : Integer renames 1; -- Illegal
> 
> I don't think that renaming an object is the same as renaming
> a number literal because the literal isn't declared anywhere.
> Wheras I could say that a returned object is declared as part
> of the function declaration.

Oh, if that is a problem then take this instead:

    X : Integer renames -1; -- Still illegal, though not a literal

But clearly your argument is nonsensical, literal is a syntactic element,
of which semantics is as much object as any of any other expression. It
would be a very perverse idea to try to draw a line between literals and
non-literals. Note also that Ada's renaming has conceptually little to do
with objects. Consider:

   X : T;
   X : T renames X; -- Illegal

though the "object" is obviously same. Same object, same name, what was
wrong?

>>    function Very_Positive return Integer is
>>    begin
>>        return -1;
>>    end Very_Positive;
>> 
>>    Oops : Positive renames Very_Positive; -- This is OK!
> 
> So is
> 
>   if 42 not in Boolean'pos(false) .. Boolean'pos(true) then
>       raise Constraint_Error;
>   end if;

You missed the point. The renaming in my example shall *not* raise
Constraint_Error. It is a clear language design fault.

Renaming is completely broken in Ada. It creates new objects, it violates
contracts, it introduces names conflicts.

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