[Newbies] Re: Adding methods to Integers...

[Bert Freudenberg]

On Apr 13, 2007, at 14:35 , Klaus D. Witzel wrote:

> On Fri, 13 Apr 2007 13:39:08 +0200, Bert Freudenberg wrote:
>
>> On Apr 13, 2007, at 13:27 , Klaus D. Witzel wrote:
>>
>>> Hi Bert,
>>>
>>> on Thu, 12 Apr 2007 18:31:55 +0200, you wrote:
>>>
>>>> This is actually wrong.
>>>
>>> :)
>>>
>>>> Only SmallIntegers are special [*].
>>>>
>>>> What happens is this: When you add two SmallIntegers (like "3 +  
>>>> 4"), and the result is a SmallInteger, the result is calculated  
>>>> in the bytecode directly. Otherwise, a regular send of #+ is  
>>>> performed.
>>>
>>> Right.
>>>
>>>> From there, everything else happens in the image,
>>>
>>> Not really. (Integer>>#+ aNumber) sends (self digitAdd: aNumber)  
>>> which is implemented as <primitive: 'primDigitAdd' module:  
>>> 'LargeIntegers'> which is part of the VM. Of course the  
>>> LargeIntegers module may be absent, have failed to load, may not  
>>> like the argument, etc.
>>
>> No, this is an *optional* primitive. It's there purely to speed up  
>> computation and can be safely removed.
>
> Sure, but this thread is not about what happens when the optional  
> primitive is removed, and I was not reflecting that, either. I was  
> rather discussing the point when the primitive does *not* fail on  
> one of Patrick's subclasses and, what the returned species is.
>
>> You could change the Integer classes to handle subclasses properly  
>> (via species etc.). So far, this has not been necessary. My point  
>> was that this (unlike SmallIntegers) is *not* hard-coded in the VM.
>
> I think it depends on operand order. When the LargeIntegers module  
> is invoked (in my previous example when sending + myLargeInteger to  
> SmallInteger 1) then a "hard-coded" instance of  
> LargePositiveIntegers is returned.
>
> The attached class can be used (together with my previous example)  
> to illustrate my point. The class does not inherit from some  
> default large integer class and the primitive does not fail,  
> regardless of operand order. I hope I didn't base my argument on a  
> bug or mistake.

I don't see your point. Do you want the primitive to fail for your  
class? This is outside of its spec, so to say. Do not use the  
primitive if you are not satisfied with its behavior.

> FWIW I do not disagree with anything about your argument, except a  
> bit with "hard-coded".

It is not hard-coded in the VM, exactly as I wrote above.  
SmallInteger arithmetic is hard-coded: There is no way to generally  
redefine SmallInteger>>+ unless you modify the bytecode interpreter,  
because method is never actually activated unless you use #perform:,  
or the result is not a SmallInteger.

But you are free to redefine what happens outside the realm of  
SmallIntegers. Invokation of the LargeInteger primitives is  
voluntary, you are not forced to use them.

- Bert -