oh, ok, I undestand now :-)... it is to show the limitations in Java.

Thanks!

On Thu, Jun 16, 2011 at 12:08 PM, Alexandre Bergel <alexandre.bergel@me.com> wrote:
> I agree with Alex, but I don't see why, alex, you say it is a good example for teaching OO (the smalltalk factorial implementation...)

This is not something that can be done in Java, the language used for teaching OO in my university.
Having methods like #abs, #factorial, #+ defined on Integer is an excellent reason why we do not need a class java.util.Math.

These methods look natural to us, but they are not for other people.

> For me is a good example of a recursive "function"

I agree with you.

> I think it would be a good OO example it it was using "object recursion" or the one that could be implemented in a prototyped language... why do you think it is a good oo example the smalltalk factorial implementation?

Because it is a natural distribution of responsibility, that cannot be easily done in Java or C#.

Alexandre


> On Thu, Jun 16, 2011 at 9:52 AM, Alexandre Bergel <alexandre.bergel@me.com> wrote:
> Hi Sven,
>
> I am not sure it should replace the standard implementation. Integer>>factorial is essentially there for teaching purpose in my opinion. I am not sure how often factorial is used in practice. The most important for me is not it to be fast, but to be an excellent example of OOP.
>
> Your implementation could be next to the standard one though.
>
> Cheers,
> Alexandre
>
>
> On 16 Jun 2011, at 06:38, Sven Van Caekenberghe wrote:
>
> > Hi,
> >
> > On Planet Smalltalk I read about this challenge: http://www.parcplace.net/list/vwnc-archive/1106/msg00080.html the goal being to optimize the current, naive Integer>>#factorial implementation.
> >
> > I had some old Lisp code hanging around, implementing an algorithm that I once found somewhere, and I ported it to Smalltalk. I am sure there are faster solutions, but this one is twice as fast as the original while still being easy to understand and it has a useful, safe helper method:
> >
> > Integer>>#svcFactorial
> > � � � "Answer the factorial of the receiver."
> >
> > � � � self = 0 ifTrue: [ ^ 1 ].
> > � � � self > 0 ifTrue: [ ^ 1 productUpTo: self ].
> > � � � self error: 'Not valid for negative integers'
> >
> > Integer>>#productUpTo: anInteger
> > � � � "Answer the product of all integers from the receiver (non-inclusive) up to anInteger (inclusive)."
> >
> > � � � | difference split |
> > � � � self assert: (self between: 0 and: anInteger).
> > � � � "the idea is to multiply LargePositiveIntegers of approximately the same size"
> > � � � difference := anInteger - self.
> > � � � difference = 0 ifTrue: [ ^ 1 ].
> > � � � difference = 1 ifTrue: [ ^ anInteger ].
> > � � � difference = 2 ifTrue: [ ^ (anInteger - 1) * anInteger ].
> > � � � difference = 3 ifTrue: [ ^ (anInteger - 2) * (anInteger - 1) * anInteger ].
> > � � � difference = 4 ifTrue: [ ^ (anInteger - 3) * (anInteger - 2) * (anInteger - 1) * anInteger ].
> > � � � split := (self + anInteger) bitShift: -1.
> > � � � ^ (self productUpTo: split) * (split productUpTo: anInteger)
> >
> > Would it be a good idea to replace the current implementation with this one ?
> >
> > Sven
> >
> >
>
> --
> _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:
> Alexandre Bergel �http://www.bergel.eu
> ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
>
>
>
>
>
>
>
>
>
> --
> Hern�n Wilkinson
> Agile Software Development, Teaching & Coaching
> Mobile: +54 - 911 - 4470 - 7207
> email: hernan.wilkinson@10Pines.com
> site: http://www.10Pines.com
>

--
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Alexandre Bergel �http://www.bergel.eu
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--
Hern�n Wilkinson
Agile Software Development, Teaching & Coaching
Mobile: +54 - 911 - 4470 - 7207
email: hernan.wilkinson@10Pines.com
site:�http://www.10Pines.com