How To Fix CL059 - You cannot extend classes using reference characteristics

SAP Error Message - Details

• Message type: E = Error

• Message class: CL - Classification

• Message number: 059

• Message text: You cannot extend classes using reference characteristics

What causes this issue?

You want to add a <DS:GLOS.reference_characteristic>reference
characteristic</> to a class. The reference characteristic is linked to
a field in the master record of the object you want to classify. For
classes of this class type, the field value is stored both in the
object master record and in classification tables.
Objects have already been allocated to the class. Therefore you can no
longer add characteristics that have a link to a field in master data
tables as this would cause inconsistencies.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.

Smart SAP Assistant

• What is the cause and solution for SAP error message CL059 - You cannot extend classes using reference characteristics ?

  The SAP error message CL059, which states "You cannot extend classes using reference characteristics," typically occurs in the context of ABAP Object-Oriented programming when you are trying to extend a class that has reference characteristics (like reference types) in a way that is not allowed by the ABAP language rules.
  Cause:
  The error arises when you attempt to create a subclass of a class that has reference characteristics (like reference variables or reference types) and you try to extend it in a manner that is not permissible. In ABAP, reference types cannot be extended in the same way as value types. This restriction is in place to maintain the integrity of the reference types and their behavior.
  Solution:
  To resolve this error, consider the following approaches:
  
  
  Check Class Definition: Review the class you are trying to extend. Ensure that you are not trying to extend reference types in a way that is not allowed. If the class has reference characteristics, you may need to rethink your design.
  
  
  Use Composition Instead of Inheritance: If you need to use reference types, consider using composition instead of inheritance. This means that instead of extending the class, you can create a new class that contains an instance of the original class as an attribute.
  
  
  Refactor Your Code: If you are trying to add functionality to a class with reference characteristics, consider refactoring your code to avoid the need for inheritance. You might create utility methods or use interfaces to achieve the desired behavior.
  
  
  Check for Abstract Classes: If the class you are trying to extend is abstract, ensure that you are implementing all the required methods in your subclass.
  
  
  Consult Documentation: Review the SAP documentation for any specific guidelines or restrictions related to class inheritance and reference types.
  
  
  Related Information:
  
  ABAP Object-Oriented Programming: Understanding the principles of object-oriented programming in ABAP can help you design your classes more effectively.
  Reference Types vs. Value Types: Familiarize yourself with the differences between reference types and value types in ABAP, as this will help you understand the limitations and capabilities of your classes.
  SAP Community and Forums: If you continue to face issues, consider reaching out to the SAP community or forums where other developers may have encountered similar issues.
  
  By following these steps, you should be able to resolve the CL059 error and design your classes in a way that adheres to ABAP's object-oriented principles.