Modularization Techniques

Subroutines, function modules and methods, how parameters are passed, and where BAPIs fit.

ABAP offers several ways to break processing into reusable units, reflecting its long history. They suit different purposes.

Three mechanisms

Mechanism	Defined in	Reuse scope	Recommended?
Subroutine (FORM)	A program	Within the program	No — legacy
Function module	A function group	System-wide	Depends on purpose
Method	A class	System-wide	Yes

Function modules

Parameter kinds

Kind	Direction	Note
IMPORT	In	Values the function receives
EXPORT	Out	Values the function returns
CHANGING	In and out	The caller variable is modified
TABLES	In and out	Internal tables, an older style
EXCEPTIONS	Error	Surfaced to the caller as sy-subrc

Calling a function module

CALL FUNCTION 'Z_CALCULATE_DISCOUNT'
  EXPORTING
    iv_amount     = lv_amount
  IMPORTING
    ev_discount   = lv_discount
  EXCEPTIONS
    invalid_input = 1
    OTHERS        = 2.

IF sy-subrc <> 0.
ENDIF.

RFC-enabled functions and BAPIs

Common BAPIs

BAPI	Purpose
BAPI_MATERIAL_SAVEDATA	Create or change a material
BAPI_SALESORDER_CREATEFROMDAT2	Create a sales order
BAPI_PO_CREATE1	Create a purchase order
BAPI_ACC_DOCUMENT_POST	Post an accounting document
BAPI_GOODSMVT_CREATE	Post a goods movement
BAPI_TRANSACTION_COMMIT	Commit; required after any BAPI

Methods

A method with RETURNING

CLASS lcl_calculator DEFINITION.
  PUBLIC SECTION.
    METHODS calculate_total
      IMPORTING it_items        TYPE ty_items
      RETURNING VALUE(rv_total) TYPE i.
ENDCLASS.

DATA(lo_calc) = NEW lcl_calculator( ).
DATA(lv_total) = lo_calc->calculate_total( lt_items ).

A method with a RETURNING parameter can be used inside an expression, which removes temporary variables. Only one is allowed, and that constraint encourages methods that do one thing.