How To Fix W8109 - Reference types '&1' and '&2' are not compatible (expression '&3')

SAP Error Message - Details

• Message type: E = Error

• Message class: W8 - Workflow: Expressions, data flow

• Message number: 109

• Message text: Reference types '&1' and '&2' are not compatible (expression '&3')

What causes this issue?

The two partners of the value assignment in the binding must have
compatible references.
If an expression or element is created with a
<DS:GLOS.3526B0B8AFAB52B9E10000009B38F974>data type reference</> to an
ABAP Dictionary table field (data type reference "D") and the other
expression or the other element references an object (data type
reference "O"), a value assignment is not possible.
Constants, or expressions, which do not begin with the characters
<(>&<)> or % are regarded as a data type reference to an ABAP
Dictionary field.

How to fix this error?

You should use the F4 input help for the binding definition.
You should only select container elements which F4 input help shows as
<ZH>Data type identical</> or </>data type</><ZH>compatible</>. Such
elements are highlighted with colors.

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

INCLUDE NA_WF_FARBLEGENDE OBJECT DOKU ID TX

Error message extract from SAP system. Copyright SAP SE.

Smart SAP Assistant

• What is the cause and solution for SAP error message W8109 - Reference types '&1' and '&2' are not compatible (expression '&3') ?

  Certainly! Here's a detailed explanation for the SAP error message:
  
  SAP Error Message:
  W8109 Reference types '&1' and '&2' are not compatible (expression '&3')
  
  Cause:
  This warning message occurs when there is an attempt to assign or compare two reference variables (objects or data references) of incompatible types in ABAP. The system detects that the reference types involved in the operation do not match or are not compatible according to the ABAP type system.
  For example, this can happen in statements like:
  
  Assigning one reference variable to another (<ref1> = <ref2>) where the types differ.
  Comparing two references of different types.
  Passing references of incompatible types to a method or function expecting a specific reference type.
  
  The placeholders in the message mean:
  
  &1 = Type of the first reference variable
  &2 = Type of the second reference variable
  &3 = The expression or statement where the incompatibility occurs
  
  
  Explanation:
  In ABAP, reference variables must be compatible in type to be assigned or compared directly. For example, a reference to a class CL_FOO cannot be assigned to a reference of class CL_BAR unless there is an inheritance relationship or explicit casting.
  
  Solution:
  
  
  Check the types of the reference variables involved in the expression indicated by &3.
  
  Use the ABAP debugger or look at the code to identify the types of &1 and &2.
  
  
  Ensure type compatibility:
  
  If the references are to classes, check if one class is a subclass of the other.
  If they are unrelated, you cannot assign or compare them directly.
  
  
  
  Use explicit casting if appropriate:
  
  
  Use CAST or TRY ... CAST to convert one reference type to another if there is an inheritance relationship.
  
  
  Example:
  DATA ref_foo TYPE REF TO cl_foo.
  DATA ref_bar TYPE REF TO cl_bar.
  
  ref_foo = CAST cl_foo( ref_bar ).
  
  
  This will only work if cl_bar is a subclass of cl_foo or vice versa.
  
  
  
  
  Adjust the code logic:
  
  If the references are fundamentally incompatible, redesign the code to avoid such assignments or comparisons.
  Use interfaces or common base classes if polymorphism is needed.
  
  
  
  Check method signatures:
  
  If the error occurs when passing parameters, verify that the method or function expects the correct reference type.
  
  
  
  
  Related Information:
  
  
  ABAP Reference Variables:
  
  Reference variables point to objects or data in memory. Their type must be compatible for assignment or comparison.
  
  
  Inheritance and Polymorphism:
  
  Reference compatibility depends on class inheritance. A reference to a subclass can be assigned to a reference of a superclass, but not vice versa without casting.
  
  
  Casting in ABAP:
  
  Use CAST or TRY ... CAST to convert references safely.
  
  
  SAP Note / Documentation:
  
  Check SAP Help Portal or relevant SAP Notes for specific issues related to reference type compatibility.
  
  
  
  Example:
  DATA ref1 TYPE REF TO cl_gui_alv_grid.
  DATA ref2 TYPE REF TO cl_gui_custom_container.
  
  ref1 = ref2. " This will cause W8109 if cl_gui_custom_container is not compatible with cl_gui_alv_grid
  Fix:
  ref1 = CAST cl_gui_alv_grid( ref2 ). " Only if cl_gui_custom_container inherits from cl_gui_alv_grid
  
  If you provide the exact code snippet or context where the error occurs, I can help you with a more precise solution.