Re: Negative float problem

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

On 02 Nov 2005 08:32:21 -0500, Robert A Duff wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> On Wed, 02 Nov 2005 10:04:21 +0100, Maciej Sobczak wrote:
>> 
>>> Dmitry A. Kazakov wrote:
>>> 
>>>> package A is
>>>>    type Foo is ...;
>>>>    function "+" (Left, Right : Foo)  return Foo;
>>>> end A;
>>>> -------------------
>>>> package A.B is
>>>>    X : Foo;
>>>>    function "+" (Left, Right : Foo)  return Foo;
>>>> end A.B;
>>>> ------------------
>>>> with A.B;
>>>> ...
>>>> A.B.X + A.B.X  -- BOOOOM!
>>> 
>>> With ADL, I would expect it to call A."+".
>> 
>> Which perfectly illustrates why there should be no such thing as ADL.
>> Exactly to prevent making the above legal with the meaning A."+".
> 
> Well, perhaps, but the above example is confusing with the current
> rules, too.  If you say "use type A.Foo", you get one "+", when you
> might expect to get the other.  Even worse, add this to A.B:
> "subtype Foo is A.Foo", and then say "use type A.B.Foo" -- you might be
> surprised to get A."+".

Because "use type" is also a kludge. (:-))

> I think the answer is a coding convention: If you want to declare an
> operator, always make it a primitive of the interesting type involved.
> I'm not sure whether that could reasonably be a language rule...

I think that non-primitive operations should be outlawed in specifications.
I mean as a language design goal, because this would also require handling
multiple dispatch and operations which are primitive for more than one
type. Then there is a case of class-wide operations...

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