Widening Cast

[andy_dingfelder3]

Hi,

i´m completly confused concerning the widening cast. The following example example won´t work. But why?

Class ZCL_BMW is a subclass of class ZCL_CAR so I though that the widening cast from CAR to BMW will work....

Any ideas, whats wrong in this example?

Regards Andy

REPORT  ztest_widening_cast.

DATA: lr_car TYPE REF TO zcl_car,
      lr_bmw TYPE REF TO zcl_bmw.

CREATE OBJECT lr_car.

CATCH SYSTEM-EXCEPTIONS move_cast_error = 1.
  lr_bmw ?= lr_car.
ENDCATCH.

[naimesh_patel]

It would not work, because this code will not set all the attributes of the LR_BMW and which will make the object incomplete and it will give you casting error.

  LR_BMW ?= LR_CAR

Try to use the TRY .. CATCH.. ENDTRY block instead of the obsolute syntax CATCH .. ENDCATCH.

DATA: lr_car TYPE REF TO zcl_car,
      lr_bmw TYPE REF TO zcl_bmw,
      lr_merc TYPE REF TO zcl_bmw,  " also subclass of the ZCL_CAR
      lo_cast_error TYPE REF TO cx_sy_move_cast_error.

* widening cast
  CREATE OBJECT lr_car.
  TRY.
       lr_bmw ?= lr_car.
    CATCH cx_sy_move_cast_error INTO lo_cast_error.
      WRITE: / 'Widening cast failed 1'.
  ENDTRY.

  CREATE OBJECT lr_merc.
  lr_car = lr_merc.  " all the Attributes of the ZCL_BMW
  TRY.
       lr_bmw ?= lr_car.
    CATCH cx_sy_move_cast_error INTO lo_cast_error.
      WRITE: / 'Widening cast failed 2'.
  ENDTRY.

You might want to check this out: [Widening Cast|http://help-abap.blogspot.com/2008/09/abap-objects-widening-cast-down-casting.html]

Regards,

Naimesh Patel

[andy_dingfelder3]

> It would not work, because this code will not set all the attributes of the LR_BMW and which will make the object incomplete and it will give you casting error.
> 

>   LR_BMW ?= LR_CAR
> 
> 
> Try to use the TRY .. CATCH.. ENDTRY block instead of the obsolute syntax CATCH .. ENDCATCH.
> 

> DATA: lr_car TYPE REF TO zcl_car,
>       lr_bmw TYPE REF TO zcl_bmw,
>       lr_merc TYPE REF TO zcl_bmw,  " also subclass of the ZCL_CAR
>       lo_cast_error TYPE REF TO cx_sy_move_cast_error.
> 
> * widening cast
>   CREATE OBJECT lr_car.
>   TRY.
>        lr_bmw ?= lr_car.
>     CATCH cx_sy_move_cast_error INTO lo_cast_error.
>       WRITE: / 'Widening cast failed 1'.
>   ENDTRY.
> 
>   CREATE OBJECT lr_merc.
>   lr_car = lr_merc.  " all the Attributes of the ZCL_BMW
>   TRY.
>        lr_bmw ?= lr_car.
>     CATCH cx_sy_move_cast_error INTO lo_cast_error.
>       WRITE: / 'Widening cast failed 2'.
>   ENDTRY.
> 
> 
> You might want to check this out: Widening Cast
> 
> Regards,
> Naimesh Patel

Hi,

thanks for your detailed answer. It seems that I misunderstand the princip of widening cast. But thanks to your answer it´s clear to me now!.

Cheers,

Andy