topic Re: Persistent export variable; is this a bug? in Application Development and Automation Discussions

Persistent export variable; is this a bug?

anthony_bateman3 — Tue, 05 Nov 2013 08:21:54 GMT

I have some code in a public instance method. I discovered that the exporting parameter ex_is_negative, once set to TRUE stays TRUE when the method is called repeatedly in a loop:

Is this expected behavior? By default, I would have expected that the variable, being an export variable, should be initialized each time the method enters, but obviously this is not the case.

Do people consider this a bug or normal behavior? Maybe failing to initialize all export parameter variables is not good practice, but languages such as Java would not allow this to happen.

Re: Persistent export variable; is this a bug?

FredericGirod — Tue, 05 Nov 2013 08:38:57 GMT

Hi,

this is an Exporting or a Changing parameter ?

I will be surprise for exporting, not surprise for changing.

regards

Fred

Re: Persistent export variable; is this a bug?

anthony_bateman3 — Tue, 05 Nov 2013 08:46:11 GMT

Hi,

It's an exporting parameter; that's why I didn't initialize it; I assumed it would be initialized each time the method is entered.

Re: Persistent export variable; is this a bug?

nabheetscn — Tue, 05 Nov 2013 08:54:30 GMT

Hi Anthony

Can you please share with us the screen shot of the parameter declaration

Thanks

Nabehet

Re: Persistent export variable; is this a bug?

Former Member — Tue, 05 Nov 2013 08:55:00 GMT

It will automatically be initialized each time the method is called.

Can you share the code for definition, implementation and object creation with call to method?

Re: Persistent export variable; is this a bug?

matt — Tue, 05 Nov 2013 09:12:55 GMT

It is not what I would expect ... but it is what happens. I have encountered this as well. Exporting parameters seem to be behaving exactly like changing parameters.

I think it is a bug. However it is documented

"An output parameter that is defined for the reference transfer is not initialized when the method is called. Therefore, no read access to it should take place before the first write access. "

To those who think it doesn't work like this, try this program:

REPORT.

TYPE-POOLS: abap.

*----------------------------------------------------------------------*

* CLASS test DEFINITION

*----------------------------------------------------------------------*

CLASS test DEFINITION.

PUBLIC SECTION.

METHODS truefalse EXPORTING flag TYPE abap_bool.

ENDCLASS. "test DEFINITION

*----------------------------------------------------------------------*

* CLASS test IMPLEMENTATION

*----------------------------------------------------------------------*

CLASS test IMPLEMENTATION.

METHOD truefalse.

WRITE: / 'Value of flag at start', flag.

IF flag EQ abap_false.

flag = abap_true.

ENDIF.

ENDMETHOD. "truefalse

ENDCLASS. "test IMPLEMENTATION

END-OF-SELECTION.

DATA: test TYPE REF TO test.

CREATE OBJECT test.

DATA: flag TYPE abap_bool.

test->truefalse( IMPORTING flag = flag ).

flag = abap_false.

SKIP.

WRITE: / 'Flag set to false'.

test->truefalse( IMPORTING flag = flag ).

flag = 'F'.

SKIP.

WRITE: / 'Flag set to F'.

test->truefalse( IMPORTING flag = flag ).

Re: Persistent export variable; is this a bug?

anthony_bateman3 — Tue, 05 Nov 2013 09:48:22 GMT

Hi,

Here's the method signature:

Definition of object:

Call to method in loop:

Re: Persistent export variable; is this a bug?

anthony_bateman3 — Tue, 05 Nov 2013 09:57:07 GMT

There you have it - thanks! I don't agree with this; it means that I need to explicitly initialize exporting parameters from now on. My failing to read the small print was the root cause .

Do you think that is bad language design, or is there a good reason for that behavior, do you think?

Re: Persistent export variable; is this a bug?

matt — Tue, 05 Nov 2013 10:06:08 GMT

I think it is conceptually incorrect. I can't think of a good reason.

Re: Persistent export variable; is this a bug?

Former Member — Tue, 05 Nov 2013 10:06:35 GMT

Hi Anthony,

You will need to add the code to export value for both cases.

if ls_t156-shkzg = c_debit.

ex_is_negative = c_true.

else.

ex_is_negative = c_false.

endif.

Re: Persistent export variable; is this a bug?

Former Member — Tue, 05 Nov 2013 10:10:14 GMT

Definitely it does not sound logical, that values are passed to the method through exporting parameters. For that we have importing and changing parameters. Flow of information should be unidirectional for importing and exporting parameters.

However, on a positive note, Anthony, you don't have to initialize the parameter each time you use the method, since you are not reading directly from this parameter in the method. You just need to make sure both cases are handled in your method. Refer the code I have given above.

Re: Persistent export variable; is this a bug?

anthony_bateman3 — Tue, 05 Nov 2013 10:12:24 GMT

Hi,

Yes I did that already thanks 🙂 This is really to follow up WHY the language has been designed to behave that way...