Loose typing and work with output parameters in function/method inner logic may be fatal

The Story

I was looking for a function to get month’s name from a date and I found HR_IN_GET_DATE_COMPONENTS.

In test mode it looked good and I wrote something like this:

    CALL FUNCTION 'HR_IN_GET_DATE_COMPONENTS'
      EXPORTING
        idate                         = `20150101` 
      IMPORTING
        ltext                         = lv_month_name
      EXCEPTIONS
        input_date_is_initial         = 1
        text_for_month_not_maintained = 2.

sy-subrc = 2

Oh, oh! In test mode I got ‘January’, but now I get a text_for_month_not_maintained exception.

Error * Error * Error = Success

I’ve debugged the code and found something weird

Problems:

1. MONTH is defined as REFERENCE(MONTH) TYPE C in function header, without lenght, but in line 36 is used as a lenght 2 char.
2. Use exporting params as working variables
3. But the worst thing, related to problem #1, is that the type of the exporting params changes depending on which parameters are assigned

Call the function with all export params fixed the problem

    CALL FUNCTION 'HR_IN_GET_DATE_COMPONENTS'
      EXPORTING
        idate                         = `20150101` 
      IMPORTING
        day                           = lv_day 
        month                         = lv_month
        year                          = lv_year 
        ltext                         = lv_month_name
      EXCEPTIONS
        input_date_is_initial         = 1
        text_for_month_not_maintained = 2.

January

Here, there are the same problems, but MONTH is supplied and now its type is CHAR2, so everything is OK

Epiologue

• Don’t be lazy, proper typing is mandatory
  • If you try to avoid unnecesary casting before function/method calls you can loose typing but you MUST cast ASAP to a typed variable.
• Don’t trust function test mode
  • In test mode, system is calling conversion routines under the hood
  • In test mode, all params are supplied and params type may be “not obvious”
• Using paramas as working variables may be harmful
  • Clear exporting params ASAP
  • Use local variables instead params for inner logic. Proper typing may mitigate this, but think in params as initial/final state and bind intermediate states (inner logic) to local variables. In case of error or unexpected behavior, it’s safer maintain output params unpolluted