gistfile1.rb

class A
  def foo
    "<3"
  end
end

class B < A
  def foo
    # super will still call A#foo, even after the method is aliased
    super * 2
  end

  alias :old_foo :foo

  def foo
    "o_O"
  end
end

puts A.new.foo     # => <3
puts B.new.old_foo # => <3<3
puts B.new.foo     # => o_O