Re: Overriding puzzle

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 15-12-31 01:10 , Randy Brukardt wrote:
> <marciant@earthlink.net> wrote in message
> news:677d0956-63d3-4de8-a6e5-b79c52a1dc12@googlegroups.com...
>> On Wednesday, December 30, 2015 at 1:24:06 PM UTC-5,
>> gautier...@hotmail.com wrote:
>>> No, the "A'Class(o)" also makes the difference when type Custom
>>> is framed into a package:
>>
> ...
>> General note to self: tagged type operations that call other operations of
>> the type should always(?) convert the object to its 'class so as to cause
>> dispatching.  Not doing so is probably a defect!
>
> Nooooo. Redispatching is best left for very limited circumstances. There's a
> reason that Ada makes you write it explicitly!

Close to an extreme view, in the spectrum of views... But I agree that 
it is good that Ada requires an explicit indication of redispatching.

> 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.

The conclusion would be that one cannot reason in any useful way about 
any dispatching call. I don't agree with that conclusion.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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