Equivalent for Row_Number() in SAP ABAP

When you want to modify the contents and store them into table and also to add a column for the value, use something like

DATA: my_string TYPE String

LOOP AT itab INTO wa_itab.
my_string = sy-tabix.
CONCATENATE some_text my_string more_text into wa_itab-my_field.
MODIFY itab FROM wa_itab.
CLEAR my_string.