In Ruby 1.8.4, 1.8.5, and as of 1.9.0 (2006-04-15):

class A < String
  attr_accessor :x
end

a = A.new 'hello'
a.x = 5
s = Set[a]
puts a.x # => 5
puts s.to_a[0].x # => nil

I would expect the second puts to return 5, not nil.  In fact, I'd expect s.to_a[0] to return the same object as a.

Date: 2007-08-11 19:14
Sender: Shyouhei Urabe

Assigning to matz; see [ruby-core:9716]