Magnitude presume that < is a total order relationship
https://en.wikipedia.org/wiki/Total_order

For point, <= is not a total order.
It might be that neither a <= b nor b <= a
So Point is not a good candidate for Magnitude
(side note: we had enough problems with Float nan which is unordered!)

In short, why changing < is not a good idea?
1) there's no natural definition of <=
2) it breaks expectations

In longer form:

We could define some total order (Matlab did it for complex), there are
infinitely many possible definitions, like sort x first, then y, or radius
first, then angle, etc...
But it's not a good idea because there is no natural relation order, an
order that mix well with arithmetic like:

(a <= b and: [c <= d]) ==> ((a+c) <= (b+d))
Current definition of = has this property, but it's not total

Currently, I presume the usage in graphics are kind of testing if inside a
bounding box with
p >= topLeft and: [p <= bottomRight]
So I'm not amazed that we can easily break things by modifying such basic
method.

In Matlab, defining < on complex has practically no interest (except when
there's small imaginary residuals), but prevents programs to fail, delaying
detection of errors.
For me, the most suspicious decision is to authorize Point < Number or
Number < Point, just because we can (or just because it's a side effect of
authorizing Point+Number).
It should rarely be usefull, and is going to wicken detection of errors

2016-08-19 10:44 GMT+02:00 marcel.taeumel <Marcel.Taeumel at hpi.de>:

> Hi, there.
>
> Right now, this is can happen when comparing two points:
>
> (100 at 50) < (100 at 60). "false"
> (100 at 50) > (100 at 60). "false"
> (100 at 50) = (100 at 60). "false"
>
> This is because one component is the same and implementation in Point is
> like this:
>
> < anotherPoint
>    ^x < aPoint x and: [y < aPoint y]
>
> Hence, points do not have like magnitudes. For the aformentioned examples,
> a
> "fix" could be:
>
> < anotherPoint
>    ^(self >= anotherPoint) not
>
> Now, the interesting thing is that event handling (mouse clicks etc.)
> becomes awkward after that. :-D
>
> Best,
> Marcel
>
>
>
>
>
>
> --
> View this message in context: http://forum.world.st/Could-a-
> Point-behave-like-a-Magnitude-tp4911882.html
> Sent from the Squeak - Dev mailing list archive at Nabble.com.
>
>
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