SAP IMMUTABLE VARIABLES - Guide

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Immutable Variables

ABAP_BACKGROUND
An immutable variable is a special variable that can be assigned a value at exactly one write position of a context which cannot be changed at other write positions. Immutable variables can be declared inline with the declaration operator FINAL.

ABAP_RULE
Consider using immutable variables
Whenever you want a variable to be filled at exactly one write position and to be read only at all other positions, use an immutable variable.

ABAP_DETAILS
An immutable variable prevents unwanted changes to the value of a variable. It combines the robustness of a constant with the flexibility of filling it at any write position. When reading the value of an immutable variable, it is guaranteed that it is filled with the value assigned during the inline declaration and that no other write access can have happened in between. If you are declaring an immutable variable inside a loop, you can be sure that its value is stable for each loop pass.

ABAP_EXAMPLE_BAD
An internal table is declared inline with the declaration operator DATA and filled with values that are not expected to be changed any more. TYPES primary_colors TYPE HASHED TABLE OF string
WITH UNIQUE KEY table_line.

DATA(primary_colors) = VALUE primary_colors( ( `yellow` )
( `red` )
( `blue` ) ).
ABAP_EXAMPLE_END

ABAP_EXAMPLE_GOOD
Using the declaration operator FINAL, an immutable table is created, where any later change of the content is prevented in the current context.
ABEXA 01671
ABAP_EXAMPLE_END