You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: extension_builder.rb
    path of file: ./repos/v8eval/ruby/lib/setup
    
    the code of the file until where you have to start completion: # BuildTool is a util class that is used to do some 
    
  def build_ext
    Dir.chdir @rb_ext_v8eval_dir do
      system('ruby extconf.rb')
      system('make')
      system('cp -r ' + @rb_ext_v8eval_dir + ' ' + @rb_lib_dir)
    end
  end