[squeak-dev] Re: intersect: when intsersects: is false
Lou at Keystone-Software.com
Mon Jun 21 19:14:55 UTC 2010
On Mon, 21 Jun 2010 21:02:29 +0200, Frank Shearar
<frank.shearar at angband.za.org> wrote:
>On 2010/06/21 16:03, Louis LaBrunda wrote:
>>>>> One could just
>>>>> leave it as it is, because the precondition for answering a "correct"
>>>>> rectangle is that the receiver and the argument intersect. If they don't, the
>>>>> answer is undefined, which means that whatever is answered is correct in a
>>>>> mathematical sense.
>>>> I urge some caution here. If "whatever is answered is correct in a
>>>> mathematical sense" is true then returning any rectangle like (100 at 100)
>>>> corner: (150 at 150) would be correct, clearly that is not the case. In
>>>> Smalltalk, nil is undefined, nil is probably the "correct" answer.
>>> Yes, this is tempting.
>>> However from a pragmatic point of view that would mean that:
>>> - either every call must be protected with an intersects: test or (...
>>> intersect ...) ifNil: [...]
>>> - or UndefinedObject must understand Rectangle protocol
>>> Answering an empty rectangle seems more simple with this respect.
>> As I don't play with rectangles much, I will defer to your better judgment.
>> Mostly I was concerned about the "whatever is answered is correct in a
>> mathematical sense" statement but maybe I was being too picky. And why I
>> quoted "correct" when I said nil was probably the "correct" answer. Correct
>> or not an empty rectangle is probably the "better" answer.
>It does occur to me that perhaps the behaviour's deliberate. Reading
>Andreas' comment in the method, it's an optimisation of a method that
>goes back to Smalltalk-76 !
>GNU Smalltalk defines the behaviour of #intersect:  as returning nil
>for non-overlapping Rectangles . (So we're already incompatible with
>another dialect!) My brief Googling didn't reveal what the other
VA Smalltalk V8 returns:
100 @ 100 corner: 50 @ 50
I don't think I like it but that is what it does. I will be interested to
see what ends up in Squeak and pass that along to Instantiations.
Keystone Software Corp.
mailto:Lou at Keystone-Software.com http://www.Keystone-Software.com
More information about the Squeak-dev