STX:

100 @ 100 corner: 50 @ 50

PrintIt:

Rectangle origin:100 at 100 extent:-50 at -50




----- Original Message ----
From: Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com>
To: Lou at keystone-software.com; The general-purpose Squeak developers list <squeak-dev at lists.squeakfoundation.org>
Sent: Mon, June 21, 2010 12:18:50 PM
Subject: Re: [squeak-dev] Re: intersect: when intsersects: is false

2010/6/21 Louis LaBrunda <Lou at keystone-software.com>:
> 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:
>>>>>> snip...
>>>>>> 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.
>>>>>> snip...
>>>>>
>>>>> 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.
>>>> Nicolas
>>>
>>> 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 [1]!
>>
>>GNU Smalltalk defines the behaviour of #intersect: [1] as returning nil
>>for non-overlapping Rectangles [2]. (So we're already incompatible with
>>another dialect!) My brief Googling didn't reveal what the other
>>Smalltalks do.
>>
>>frank
>>
>>[1]
>>http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.106.2641&rep=rep1&type=pdf
>>
>>[2]
>>http://www.gnu.org/software/smalltalk/manual-base/html_node/Rectangle_002drectangle-functions.html
>>
>
> VA Smalltalk V8 returns:
>  100 @ 100 corner: 50 @ 50
>

same as Squeak/Pharo VW and Dolphin

> 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.
>
> Lou
> -----------------------------------------------------------
> Louis LaBrunda
> Keystone Software Corp.
> SkypeMe callto://PhotonDemon
> mailto:Lou at Keystone-Software.com http://www.Keystone-Software.com
>
>
>