What's the meaning of ?= in ABAP operators?
?=
is the (down)casting operator. It's used for assignments between reference variables, whose assignability is checked as early as the runtime starts.
C.f. general explanation at wikipedia.
Example:
DATA fruit TYPE REF TO zcl_fruit.
DATA apple TYPE REF TO zcl_apple. " inherits from zcl_fruit
DATA apricot TYPE REF TO zcl_apricot. " inherits from zcl_fruit
...
case fruit->type.
when 'apple'.
apple ?= fruit.
seeds = apple->seeds.
when 'apricot'.
apricot ?= fruit.
seeds = VALUE #( ( apricot->kernel ) ).
endcase.
Since 7.40, the constructor operator CAST
may be used:
DATA fruit TYPE REF TO zcl_fruit.
...
case fruit->type.
when 'apple'.
seeds = CAST zcl_apple( fruit )->seeds.
when 'apricot'.
seeds = VALUE #( ( CAST zcl_apricot( fruit )->kernel ) ).
endcase.