A colleague was surprised that uniq didn't seem to work for instances of classes he created.

Index: array.c
===================================================================
--- array.c     (revision 11516)
+++ array.c     (working copy)
@@ -2588,6 +2588,8 @@
  *  containing elements common to the two arrays, with no duplicates.
  *
  *     [ 1, 1, 3, 5 ] & [ 1, 2, 3 ]   #=> [ 1, 3 ]
+ *
+ *  (a is a duplicate of b if a.hash == b.hash and a.eql?(b))
  */
 
 
@@ -2621,6 +2623,8 @@
  *
  *     [ "a", "b", "c" ] | [ "c", "d", "a" ]
  *            #=> [ "a", "b", "c", "d" ]
+ *
+ *  (a is a duplicate of b if a.hash == b.hash and a.eql?(b))
  */
 
 static VALUE
@@ -2661,6 +2665,8 @@
  *     a.uniq!   #=> ["a", "b", "c"]
  *     b = [ "a", "b", "c" ]
  *     b.uniq!   #=> nil
+ *
+ *  (a is a duplicate of b if a.hash == b.hash and a.eql?(b))
  */
 
 static VALUE
@@ -2694,6 +2700,8 @@
  *     
  *     a = [ "a", "a", "b", "b", "c" ]
  *     a.uniq   #=> ["a", "b", "c"]
+ *
+ *  (a is a duplicate of b if a.hash == b.hash and a.eql?(b))
  */
 
 static VALUE