インターフェイスのみimplementsできる
Symfony \ Component \ Debug \ Exception \ FatalErrorException (E_UNKNOWN) App\Cart cannot implement Gloudemans\Shoppingcart\Facades\Cart - it is not an interface
Symfony \ Component \ Debug \ Exception \ FatalErrorException (E_UNKNOWN) App\Cart cannot implement Gloudemans\Shoppingcart\Facades\Cart - it is not an interface