Re: Access types as parameters

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

On Thu, 13 Aug 2009 11:34:20 +0300, Niklas Holsti wrote:

> Randy Brukardt wrote:
> 
>> You almost never want redispatching
> 
> That's interesting as my experience is the opposite: Most of the calls 
> between primitive methods in my code use redispatching.

Shudder...

> My tagged types tend to have a hierarchy of primitive operations, for 
> example an Overall_Method that implements some functionality by a 
> sequence of calls to a Detail_Method. Some derived types override 
> Detail_Method, so the call from Overall_Method to Detail_Method must 
> redispatch. Some other (or the same) derived types override 
> Overall_Method, so it cannot be class-wide.

When this happens to me I always consider it as a strong indication to
re-design.

> Perhaps the frequency of redispatching depends on the application 
> domain, or on personal programming style. The frequency of redispatching 
> might me an interesting OO "metric".

Yes. I think the target shall be strictly 0%.

I consider re-dispatch is an indication of a language / design problem,
because it is a hidden type error. An argument goes as follows. Once you
have dispatched to some type T, the corresponding controlling parameter is
of this type. Let we converted it to a class. If now it dispatches again to
T, then that was just wasting time, if it dispatches to S /= T then it is a
type error.

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