Re: Overriding puzzle

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

On 2015-12-31 09:22, Niklas Holsti wrote:
> On 15-12-31 01:10 , Randy Brukardt wrote:

>> The model of Ada is that within a routine (including inherited routines) the
>> object acts as if it had the named type. This makes it much easier to reason
>> about the routine, as the behavior of all of the routines called is
>> known.
>>
>> When you redispatch, you no longer can reason in any useful way about the
>> behavior of the call -- essentially you are depending on "magic" (and the
>> competency of others) to get the right answer. In limited circumstances
>> (like the OP), it works well, but for general programming, look out!
>
> The same (IMO a bit paranoid) argument would logically apply to all
> dispatching calls, including dispatching calls from class-wide subprograms.

A class-wide subprogram is declared class-wide = for all types from the 
class.

> The conclusion would be that one cannot reason in any useful way about
> any dispatching call.

One can. The issue is about the types the reasoning should apply. You 
cannot reason about specific types when you potentially re-dispatch away 
from the specific type stated. But you still can reason about a subclass 
of types even if you dispatch no some of them, unknown in advance.

The point is that IF you are going dispatch THEN, please, state your 
intention in a well-typed way.

Happy New Year!

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