192 singleton method error.rb

# error occurs when same lexical method (which calls super) 
# is defined on the singleton class of two or more objects of different classes, 
# and then that method is called on any of the objects
# other than the last one the method was defined on...

def x(obj)
# uncomment eval and it works
# eval "
  class << obj
    def to_s
      super
    end
  end
# "  
end

class C1;end
class C2;end
class C3;end

o1=C1.new
o2=C2.new
o3=C3.new
# copy paste x() code for each object rather calling x() and it works
x(o1)
x(o2)
x(o3)

o3.to_s
o2.to_s  # raises: in `to_s': super from singleton method that is defined to multiple classes is not supported; this will be fixed in 1.9.3 or later (NotImplementedError)
o1.to_s  # also would raise