In JAVA, we have FINAL for making sure, a variable is assigned only once. This blog is about how to emulate this concept with ABAP

After reading, have a look at part two of this blog!

Motivation

Often, when I decide to extract a complex method into a new class, I struggle with the fact, that importing parameters should not change in the class.

Usually, I turn all the parameters into class attributes which makes the importing parameters changeable. My motivation was to avoid being able to change these attributes once they are set.

Approach

I use a little local class to keep all the immutable variables:

class read_only definition final.
  public section.
    data vbdkr type vbdkr read-only.
    data vbdpr type vbdpr read-only.
    data nast type nast read-only.

    methods constructor
      importing
        i_vbdkr     type vbdkr
        i_vbdpr     type vbdpr
        i_nast      type nast.
endclass.

CLASS read_only IMPLEMENTATION.

  METHOD constructor.
    vbdkr = i_vbdkr.
    vbdpr = i_vbdpr.
    nast = i_nast.
  ENDMETHOD.

ENDCLASS.

Since the public attributes are read-only, they can be only accessed with read.

In the entry method, I instantiate the class passing my importing variables:

    read_only = new #(  i_vbdkr = i_vbdkr
                        i_vbdpr = i_vbdpr
                        i_nast = i_nast ).

In the coding, I access the variables using the direct reference

      ls_ftechdat-vbeln = read_only->vbdkr-vbeln.
      ls_ftechdat-posnr = read_only->vbdpr-posnr.
      ls_ftechdat-vgbel = read_only->vbdpr-vgbel.

Result: as soon as I try to change the values in the read_only class, I will get a syntax error.