behave_method.rb

class Nyan
  def behave_method(target, source)
    (class << self; self end).module_exec do
      alias_method "#{target}_original", target unless method_defined? "#{target}_original"
      alias_method "#{source}_original", source unless method_defined? "#{source}_original"
      alias_method target, "#{source}_original"
    end
  end

  def with_behaving_method(a, b)
    behave_method(a, b)
    yield
  ensure
    behave_method(a, a)
  end

  def nyan
    :nyan
  end

  def nyan_extended
    :nyan_extended
  end

  def nyan_extended_extended
    :nyan_extended_extended
  end
end

nyan = Nyan.new

p nyan.nyan #=> :nyan

nyan.with_behaving_method(:nyan, :nyan_extended) do
  p nyan.nyan #=> :nyan_extented

  nyan.with_behaving_method(:nyan, :nyan_extended_extended) do
    p nyan.nyan #=> :nyan_extended_extended

    nyan.with_behaving_method(:nyan, :nyan_extended) do
      p nyan.nyan #=> :nyan_extended
    end
  end
end

p nyan.nyan #=> :nyan