From: Joel VanderWerf <vjoel@...>
Date: 2003-10-02T04:03:29+09:00
Subject: Re: Making == symmetric?

Zach Dennis wrote:
...
> on #1. I agree with Mark and I'd also like to say...why would you want
> to use the == to return true when comparing different objects, even if
> they are of the same class, with the same attributes. Unless one's a pointer
> or reference and you are using an equivalency of a === test. I don't see why
> someone would want this expected behavior from == itself.

Well, for example:

irb(main):001:0> [1,2] == [1,2]
=> true

Also, strings.

Of course, this isn't really a "class with attributes", but even for 
user defined classes, I sometimes define #== to work this way. This 
seems like the right thing to do for geometrical objects, like points. YMMV.

> 
> on #2. I think 2 different classes should always return false when compared
> to
> one another. Otherwise you are getting away from the simplicity and purpose
> of a comparison in it's most generic form and you are bringing
> in special cases where "behavior is varied". If you want to allow for
> special case scenario's then perhaps make a new comparison operator/method
> and leave == alone.

irb(main):002:0> 1.0 == 1
=> true

Or, if you had two Point classes, one maintaining its state in polar 
coordinates, and the other in cartesian coordinates, you might want 
equality to transcend class boundaries.