ruby stdlib set error

intersection.rb

class Point
  attr_reader :x, :y
  def initialize(x, y)
    @x, @y = x, y
  end
  def ==(other)
    x == other.x && y == other.y
  end
end

ary1 = [Point.new(1, 3), Point.new(2, 4)]
ary2 = [Point.new(1, 3), Point.new(3, 5)]

ary1.select{|item| ary2.include? item} #==> [<#point x=1 y=3>]
Set.new(ary1).intersection(Set.new(ary2)).to_a #==> []

The equality of each couple of elements is determined according to Object#eql? and Object#hash, since Set uses Hash as storage. (http://www.ruby-doc.org/stdlib-1.9.3/libdoc/set/rdoc/Set.html) Since they're different object refs, each points .hash() differs and thus no Set intersection.

Ahh, the old adage is true once again. If you think there is a problem with the language, you are probably wrong.