ruby_bug_12131.rb

obj1 = Object.new
def obj1.singleton_method_added(n)
  p n
end

def obj1.new_singleton_method
end
# => :singleton_method_added
# => :new_singleton_method

class Object
  def singleton_method_added(n)
    p n
  end
end

obj2 = Object.new
def obj2.new_singleton_method
end
# => :new_singleton_method

str = String.new
def str.singleton_method_added(n)
  p n
end
def str.new_singleton_method
end
# => :singleton_method_added
# => :new_singleton_method