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Date: Thu, 13 Aug 2009 23:13:39 +0300
From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Organization: Tidorum Ltd
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Subject: Re: Access types as parameters
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Date: 2009-08-13T23:13:39+03:00
List-Id: <comp.lang.ada>

Dmitry A. Kazakov wrote:
> 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...

Also an interesting reaction.

> 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.

To me that is a very abstract and formalistic argument that is easily 
weaker than the practical benefits (providing sensible but overridable 
default behaviour while avoding code duplication) that make me use 
redispatching. What is more, a central benefit of inheritance is that an 
object can be viewed as being of parent type T *and also* of derived 
type S, depending on the context and your needs, so I don't accept that 
redispatching "to a different type" implies a type error.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .