public function instance($instance = null)
    {
        $instance = $instance ?: self::DEFAULT_INSTANCE;

        $this->instance = sprintf('%s.%s', 'cart', $instance);

        return $this;
    }
public function instance($instance = null)
    {
        $instance = $instance ?: self::DEFAULT_INSTANCE;

        $this->instance = sprintf('%s.%s', 'cart', $instance);

        return $this;
    }
public function instance ( $ instance = null ) { $ instance = $ instance ? : self :: DEFAULT_INSTANCE ; $ this -> instance = sprintf ( '%s.%s' , 'cart' , $ instance ) ; return $ this ; }
Set the current cart instance.

@param string|null $instance
@return \Gloudemans\Shoppingcart\Cart
Set the current cart instance .