Finish a simple method alias, very easy implementation. super is also available in the block, it will call the same-name-method in superclass

gistfile1.rb

class A
  def f() 'This is OldA#f' end
end

puts A.new.f # => This is OldA#f

# ----------------

def alias_class_chain(cls, property, &block)
  old_class_name = "#{cls.name}Without#{property}"
  Object.send :const_set, old_class_name, cls
  Object.send :remove_const, cls.name
  Object.send :const_set, cls.name, Class.new(cls, &block)
end

alias_class_chain(A, 'Test') do
  def f() 'This is NewA#f' end
end

puts A.new.f # => This is NewA#f
puts AWithoutTest.new.f #=> This is OldA#f

alias_class_chain(A, 'NewTest') do
  def f() 'This is NewNewA#f' end
end

puts A.new.f # => This is NewNewA#f
puts AWithoutNewTest.new.f # => This is NewA#f