ABAP_to_the_Future

2
New Language Features in ABAP 7.4
ABAP Test Cockpit
Speaking of FOR ALL ENTRIES, any programmer with even a little experience will have
fallen into the trap in which FOR ALL ENTRIES can bring down your program when you
pass in an empty table. Happily, when Chap ter 4 looks at the ABAP Test Cockpit, you
will see that the syntax chec k now warns you to test that LT_MONSTERS is not empty
when doing such a thing to avoid the bug in SAP whereby an empty table retrieves the
whole database table.
2.7 Object-Oriented Programming
SAP introduced the concept of object-oriented programming in ABAP in the year
2000. Since then, it has been the recommended method of programming. This
section will describe the new features of ABAP 7.4 that relate to object-oriented
programming.
2.7.1 Upcasting/Downcasting with CAST
In OO programming, a downcast is a process in which you turn a generic object,
like a monster, into a more specific object, like a green monster. An upcast is the
reverse. This functionality has been available in ABAP for a long time, but it gets
a lot easier in 7.4.
To take a non-monster-related example for once, consider a situation where you
need to get all the components of a spec ific dictionary structure. Listing 2.69
shows how you would do this prior to ABAP 7.4. First of all, you call a method of
CL_ABAP_TYPEDESCR to get metadata about a certain structure. However, to get the
list of components of that structure into an internal table, you need an instance of
CL_ABAP_STRUCTDESCR; this is a subclass of CL_ABAP_TYPEDESCR. Thus, you need to
do a downcast to convert the instance of the parent class into an instance of the
subclass.
DATA lo_structdescr TYPE REF TO cl_abap_structdescr.
lo_structdescr ?= cl_abap_typedescr=>describe_by_name( 'ZSC_MONSTER_
HEADER' ).
DATA lt_components TYPE abap_compdescr_tab.
lt_components = lo_structdescr->components.
Listing 2.69 Components of a Specific Dictionary Structure without CAST
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