topic Re: Modify read-only static attribute from a class enhancement in Application Development and Automation Discussions

Modify read-only static attribute from a class enhancement

Former Member — Wed, 29 Apr 2015 14:25:54 GMT

Hello,

I would like to know how to modify a read-only static attribute from a class enhancement.

Example: I added GV_MY_ATTRIBUTE as a static (class) read-only attribute to the CL_A_STANDARD_CLASS class via the Z_MY_ENHANCEMENT enhancement. I added a pre-exit method to the CL_A_STANDARD_CLASS=>A_STATIC_STANDARD_METHOD static standard method via the Z_MY_ENHANCEMENT enhancement. How can I modify GV_MY_ATTRIBUTE from the pre-exit?

Of course, I don't want to create a public static setter to modify the attribute value, because I don't want it to be modifiable outside of the class.

Thanks in advance for your help!

Mathieu

Re: Modify read-only static attribute from a class enhancement

matt — Wed, 29 Apr 2015 14:30:46 GMT

Is there a problem changing GV_MY_ATTRIBUTE from your pre-exit? I can imagine there might be, due to the way enhancements to classes are handled.

Possible solutions:

Create a private static setter and call that from your pre-exit.

Define GV_MY_ATTRIBUTE as a private static, and only allow external access via a getter.

Re: Modify read-only static attribute from a class enhancement

Former Member — Wed, 29 Apr 2015 14:41:15 GMT

It won't work: if the setter is private or protected, it can not be called from within the enhancement.

Re: Modify read-only static attribute from a class enhancement

matt — Wed, 29 Apr 2015 14:56:38 GMT

Create another class which has the SAP class as a friend. Put GV_MY_ATTRIBUTE as a private static attribute of this new class, and create a public getter.... or... make GV_MY_ATTRIBUTE a public read only attribute of the new class, can create a private setter for it.

Re: Modify read-only static attribute from a class enhancement

Former Member — Wed, 29 Apr 2015 15:07:37 GMT

I'm not sure I want to create a class just for this ^^ Wouldn'it a bit weird to create a class that only contains an attribute and a setter? Isn't there a more direct, simpler method?

Isn't it possible to use the core_object enhancement object (that represents the current instance of the class that is enhanced, in other words, "me") to access the class itself?

Re: Modify read-only static attribute from a class enhancement

raphael_almeida — Wed, 29 Apr 2015 15:19:31 GMT

Hi Meister Matthew!

Excuse my ignorance but the READ ONLY statement is not only used to read the public attribute, blocking overwritten in it?

I believe that using SETTER / GETTER help in this case.

Re: Modify read-only static attribute from a class enhancement

Former Member — Wed, 29 Apr 2015 15:36:59 GMT

When an attribute is read-only, you can read it from outside its class / instance, and you can modify it only from within its class / instance.

In other words, it allows to avoid to create a getter (as the attribute is public) but without the "danger" for the attribute to be modified by "someone else" (another object / class than the object / class it belongs to).

The problem I have is that the attribute is part of a class' enhancement and the enhancement is considered as "someone else" than the class. Therefore, the only solution is to make the attribute as NON read-only, which I don't want because I don't want the attribute to be modifed outside of the class, or to create a public setter that I call from the enhancement, which I don't want either for the same reason.

Re: Modify read-only static attribute from a class enhancement

Former Member — Wed, 29 Apr 2015 16:37:52 GMT

Might a protected setter do the job?

Re: Modify read-only static attribute from a class enhancement

matt — Wed, 29 Apr 2015 17:01:39 GMT

It depends how SAP technically manage the enhancement. If it's a subclass, it should work.

Re: Modify read-only static attribute from a class enhancement

matt — Wed, 29 Apr 2015 17:04:22 GMT

Obviously that would be ideal, but the enhancement of classes isn't (as you've found) entirely straightforward - so some convoluted solution might be the only way.

I don't see a problem with creating a small class for one specific purpose. I've often done it. More often in Java, for sure, but also in ABAP.

Re: Modify read-only static attribute from a class enhancement

Former Member — Thu, 30 Apr 2015 08:20:04 GMT

As already told, "if the setter is private or protected, it can not be called from within the enhancement".

Unfortunately (?), an enhancement is not a sublcass of the enhanced class.

So I did it! I made the enhancement a sublass of the enhanced class and I have been able to modify directly the class read-only attribute, without using a public setter .

I went to my enhancement code and changed:


CLASS lcl_z_my_enhancement DEFINITION.
  PUBLIC SECTION.
[...]
ENDCLASS.                    "LCL_Z_MY_ENHANCEMENT

To:


CLASS lcl_z_my_enhancement DEFINITION INHERITING FROM cl_a_standard_class.
  PUBLIC SECTION.
[...]
ENDCLASS.                    "LCL_Z_MY_ENHANCEMENT

And then:


CLASS lcl_z_my_enhancement IMPLEMENTATION.
  METHOD constructor.
    me->core_object = core_object.
  ENDMETHOD.                    "CONSTRUCTOR

To:


CLASS lcl_z_my_enhancement IMPLEMENTATION.
  METHOD constructor.
    super->constructor( ).
    me->core_object = core_object.
  ENDMETHOD.                    "CONSTRUCTOR

After that, I have been able to do:


gv_my_attribute = a_value.

Even if gv_my_attribute is read-only.