original_string: public function instance($instance = null)
      {
          $instance = $instance ?: self::DEFAULT_INSTANCE;
  
          $this->instance = sprintf('%s.%s', 'cart', $instance);
  
          return $this;
      }
code: public function instance($instance = null)
      {
          $instance = $instance ?: self::DEFAULT_INSTANCE;
  
          $this->instance = sprintf('%s.%s', 'cart', $instance);
  
          return $this;
      }
code_tokens: public function instance ( $ instance = null ) { $ instance = $ instance ? : self :: DEFAULT_INSTANCE ; $ this -> instance = sprintf ( '%s.%s' , 'cart' , $ instance ) ; return $ this ; }
docstring: Set the current cart instance.
  
  @param string|null $instance
  @return \Gloudemans\Shoppingcart\Cart
docstring_tokens: Set the current cart instance .