1 files changed, 17 insertions, 0 deletions
diff --git a/lib/set.rb b/lib/set.rb
index bfa37d4dc0..009721381b 100644
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -475,6 +475,23 @@ class Set
     @hash.eql?(o.instance_variable_get(:@hash))
   end
 
+  # Returns true if obj is a member of the set, and false otherwise.
+  #
+  # Used in case statements:
+  #
+  #   case :apple
+  #   when Set[:potato, :carrot] then 'vegetable'
+  #   when Set[:apple, :banana]  then 'fruit'
+  #   end
+  #   #=> "fruit"
+  #
+  # Or by itself:
+  #
+  #   Set[1, 2, 3] === 2 #=> true
+  #   Set[1, 2, 3] === 4 #=> false
+  #
+  alias === include?
+
   # Classifies the set by the return value of the given block and
   # returns a hash of {value => set of elements} pairs.  The block is
   # called once for each element of the set, passing the element as