On 2010/06/20 00:58, Jim Rosenberg wrote:
> [Using Squeak 3.8; apologies if more current versions "fix" this ... ]
>
> This expression yields false:
>
> ((0 at 0) corner: (50 at 50)) intersects: ((100 at 100) corner: (150 at 150))
>
> So, what should this yield?:
>
> ((0 at 0) corner: (50 at 50)) intersect: ((100 at 100) corner: (150 at 150))
>
> I was expecting perhaps nil. Instead I got (100 at 100) corner: (50 at 50).
> This is "a surprise". It's certainly not right mathematically ...

It's still that way in trunk, at any rate.

I do think that the current behaviour's wrong.

In the interest of keeping the result of a #intersect: uniform, we could 
return Rectangle origin: (0 at 0) corner: (0 at 0) instead of nil. (And we can 
put that long expression inside a new method, 
Rectangle>>emptyRectangle.) Then we could compose multiple #intersect:s 
without special-casing anything.

I think we just need a guard clause like

     | aPoint left right top bottom |
     (self intersects: aRectangle) ifFalse: [^ self emptyRectangle].

     "Rest of #intersect goes here."

but I'm sure Nicolas Cellier will weigh in with a definitive answer :)

frank