Expression problem for ABAP program

[Former Member]

Hi everyone,

Once i have saw a expression in ABAP program. as follows.

DATA:drag_object TYPE REF TO lcl_dragdrop_dataobject.

CATCH SYSTEM-EXCEPRIONS move_cast_error = 1.

drag_object ?= dragdrop_object->object.

ENDCATCH.

IF sy-subrc = 1.

CALL METHOD dragdrop_object->abort.

EXIT.

ENDIF.

I don't know what is "?=" .

Please help me.

Thanks Advanced !

[Former Member]

Hi,

This is abap Object concept of casting. Check this link

http://help.sap.com/erp2005_ehp_03/helpdata/EN/c3/225b5f54f411d194a60000e8353423/frameset.htm

Regards

[Former Member]

Hi,

Its known as Casting Operator, you can get more details on tcode ABAPHELP and enter ?= in the coming dialog and press enter.

Regards

Karthik D

[Former Member]

Thanks your best answer !

[Former Member]

DATA: airplane TYPE REF TO lcl_airplane,

cargo_airplane TYPE REF TO lcl_cargo_airplane,

cargo_airplane2 TYPE REF TO lcl_cargo_airplane.

CREATE OBJECT cargo_airplane.

airplane = cargo_airplane.

cargo_airplane2 ?= airplane.

The type of case described above is known as a widening cast because it changes the

view to one with more details. The instance assigned (a cargo plane in the above

example) must correspond to the object reference (cargo_airplane in the above example),

that is, the instance must have the details implied by the reference. This is also known as

a u201Cdown castu201D. The widening cast in this case does not cause an error because the

reference airplane actually points to an instance in the subclass lcl_cargo_airplane. The

dynamic type is therefore u2018REF TO lcl_cargo_airplaneu2019.

The widening cast logically represents the opposite of the narrowing cast. The widening cast cannot be checked statically, only at runtime. The Cast Operator u201C?=u201D (or the equivalent u201CMOVE ... ?TO u2026u201D) must be used to make this visible.