From: Krishna Dole <kpdole@...>
Date: 2003-06-27T09:48:56+09:00
Subject: Using & for arrays of objects

Hi,
I'm having trouble using the & (intersection) method on two arrays of
objects. I know that if the objects don't have comparison methods, & won't
work because it is looking at the object IDs rather than values stored in
the objects, but I can't seem to get & to use the comparison methods I want.

Thanks,
Krishna


# A silly class that stores a single number.
class Trivial
	def initialize(n)
		@n = n
	end
	def n
		@n
	end

	# I hoped these two methods would allow & to work on arrays containing this
class.
	def ==(anOther)
		@n == anOther.n
	end
	def <=>(anOther)
		@n <=> anOther.n
	end
end

a = Trivial.new(6)
b = Trivial.new(6)

p (a == b) # this returns true, like I hoped
p (a<=>b) # this returns 0, also good

# Now make some arrays
foo = [Trivial.new(1), Trivial.new(12)]
bar = [Trivial.new(1), Trivial.new(4)]

p (foo[0] == bar[0]) # returns true
p (foo[0] <=> bar[0]) # returns 0 -- Great! everything seems to be working!

p (foo & bar) # returns an empty array! NOOOOO!!!!!