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2009/4/24 Mike Stephens <rubfor / recitel.net>:
> Robert Klemme wrote:
>>
>> The must have criterion for polymorphism is not classes but late
>> binding.
>
> I think this is where we disagree. You seem to be saying polymorphism is
> the ability for a piece of code to handle objects of differing types.

No, that's not what I said.

> I don't think that is necessary. It's perfectly alright for each
> object-type to have it's own code to handle a method.

Of course.  But this code must be *executed*.

> The only thing
> that needs to be shared is the name, not its implementation.

Correct.  And depending on the language, the signature of two methods
must be identical to be able to invoke them polymorphic.

> This works just fine in early-binding contexts.

Actually no.  My C++ is a bit rusty these days but if you do _not_
declare a method as "virtual" and have a pointer of the base class
type which points to a sub class instance the method invoked is
actually the base class's method. This can only be remediated by late
binding (declaring as "virtual") because only then the type of the
object at hand decides about the method invoked.

With the attached program you get:

09:32:19 Temp$ g++ t.cpp
09:32:36 Temp$ ./a.exe
Base:a
Base:b
Base:a
A:b
Base:a
B:b
09:32:43 Temp$

Here, only b() is invoked polymorphic.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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