Index: lib/set.rb
===================================================================
--- lib/set.rb	(Revision 17065)
+++ lib/set.rb	(Arbeitskopie)
@@ -14,13 +14,13 @@
 # == Overview 
 # 
 # This library provides the Set class, which deals with a collection
-# of unordered values with no duplicates.  It is a hybrid of Array's
+# of unordered values with no duplicates. It is a hybrid of Array's
 # intuitive inter-operation facilities and Hash's fast lookup.  If you
 # need to keep values ordered, use the SortedSet class.
 #
 # The method +to_set+ is added to Enumerable for convenience.
 #
-# See the Set class for an example of usage.
+# See the Set and SortedSet documentation for examples of usage.
 
 
 #
@@ -434,7 +434,34 @@
   end
 end
 
-# SortedSet implements a set which elements are sorted in order.  See Set.
+# 
+# SortedSet implements a Set that guarantees that it's element are
+# yielded in sorted order (according to the return values of their #<=> methods)
+# when iterating over them.
+# 
+# All elements that are added to a SortedSet must include the Comparable module.
+# 
+# Also, all elements must be <em>mutually comparable</em>: 
+# <tt>el1 <=> el2</tt> must not return <tt>nil</tt> for any elements
+# <tt>el1</tt> and <tt>el2</tt>, else an ArgumentError will be raised
+# when iterating over the SortedSet.
+#
+# == Example
+# 
+#   require "set"
+#   
+#   set = SortedSet.new(2, 1, 5, 6, 4, 5, 3, 3, 3)
+#   ary = []
+#   
+#   set.each do |obj|
+#     ary << obj
+#   end
+#   
+#   p ary # => [1, 2, 3, 4, 5, 6]
+#   
+#   set2 = SortedSet.new(1, 2, "3")
+#   set2.each { |obj| } # => raises ArgumentError: comparison of Fixnum with String failed
+#   
 class SortedSet < Set
   @@setup = false
 
@@ -459,6 +486,12 @@
 	    @hash = RBTree.new
 	    super
 	  end
+	  
+	  def add(obj)
+	    obj.is_a?(Comparable) or raise ArgumentError, "value must be comparable"
+	    super
+	  end
+	  alias << add
 	}
       rescue LoadError
 	module_eval %{
@@ -477,10 +510,10 @@
 	    super
 	  end
 
-	  def add(o)
+	  def add(obj)
+	    obj.is_a?(Comparable) or raise ArgumentError, "value must be comparable"
 	    @keys = nil
-	    @hash[o] = true
-	    self
+	    super
 	  end
 	  alias << add