Fwd: hasEqualElements:

On Thu, 24 Dec 2009, [hidden email] wrote:

> Em 24/12/2009 01:21, Levente Uzonyi < [hidden email] > escreveu:
>
>>  On Thu, 24 Dec 2009, [hidden email] wrote:
>>
>>> Em 23/12/2009 22:51, Nicolas Cellier escreveu:
>>>
>>>>  2009/12/24 :
>>>>> Igor, Sometimes  a fallacy can  be written by clever  people, by
>>>>> accident.  If you pay attention to the line: (size := self size)
>>>>> =  otherCollection  size ifFalse:  [^false].   I all  Smalltalks
>>>>> [Except  Pharo  to  what  I   wrote  a  comment  in  issue  1637
>>>>> http://code.google.com/p/pharo/issues/detail?id=1637] this would
>>>>> return  false  if  self  be  not  Collection  or  otheCollection
>>>>> isKindOf:  Collection  not.    This  happens  because  in  these
>>>>> Smalltalks Object>>size returns zero.
>>>>> Not  so sure.   Try  1.0 size,  then  1.0 at:  1.0  size in  you
>>>>  favourite
>>>> dialect.
>>> Nicolas,
>>> In Squeak 3.10.2-7179:
>>> 1.0 size -> 2 "OK I'm surprised here"
>>  It's  not surprising  since Float  is a  variable word  subclass of
>> Number. :)
>>
>>> 1.0 at: 1.0 size -> 0 "this will not work anymore in Pharo because
>>> indices have to be Integer in Pharo right now"
>>  The index is 2, so it will  work. Btw, I wonder how pharo can force
>> Integer indices if the vm accepts Floats too.
>>
> Levente,
>
> In fact VM _does_ _not_ accept Floats as indices.  There is a hack in
> Squeak code (which in fact contradicts the  comment in the method) in
> the #at: methods that make a conversion from Number to Integer.
>
> If you comment that code out you'll see the VM #at: (via the primitive)
> will fail with Floats.

True, and cool, since this hack can be removed. Now I wonder why did I
assume that the vm has this hack. :)

Levente

>
> --
> Cesar Rabak
>
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On Thu, 24 Dec 2009, Eliot Miranda wrote:
>
> This 'hack' is as old as Smalltalk-80 V2 and is AFAICT in all Smalltalk-80
> derived Smalltalks:
>
> !Object methodsFor: 'accessing'!
> at: index
>    "Answer the value of an indexable field in the receiver. Fail if the
>    argument index is not an Integer or is out of bounds. Essential. See
>    documentation in Object metaclass."
>
>    <primitive: 60>
>    index isInteger
>        ifTrue: [self errorSubscriptBounds: index].
>    (index isKindOf: Number)
>        ifTrue: [^self at: index truncated]
>        ifFalse: [self errorNonIntegerIndex]!
>
> It is also free in the sense that the failure code is only invoked when the
> primitive fails and so adds nothing to the cost of successful accesses,
> which are the high dynamic frequency operation.  It will also show up under
> profiling if one is concerned about efficiency, and so isn't a hidden cost.
>
> It is also in keeping with Smalltalk's mixed mode/arbitrary precision
> implicit coercion number system that one *can* use fractions or floats as
> indices.
>
> Stripping out coercions like this will make the system more brittle.  So
> please do *not* remove this "hack".  I think it's a feature and a useful
> one.

Can you give me an example that demonstrates the usefulness of this
feature?

Levente

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