Is it possible to create an Enumeration (enum) in ABAP?

Before release 7.51, there was no native support for enums in ABAP, but you can simulate the same behavior with a few simple steps:

1. Create your "enum" class;
2. Set the instance constructor to private;
3. Add the static attributes of TYPE REF TO <your_class> for each "enum object";
4. Create a CLASS_CONSTRUCTOR and instantiate each "enum object" with the desired properties.

For instance, if you have a status enum, you may have a CL_STATUS class with CL_STATUS=>APPROVED and CL_STATUS=>REJECTED enum objects.

Example:

REPORT z_test.

CLASS cl_status DEFINITION
      CREATE PRIVATE.
  PUBLIC SECTION.
    CLASS-DATA: approved TYPE REF TO cl_status,
                rejected TYPE REF TO cl_status.
    CLASS-METHODS class_constructor.
ENDCLASS.
CLASS cl_status IMPLEMENTATION.
  METHOD class_constructor.
    approved = NEW cl_status( ).
    rejected = NEW cl_status( ).
  ENDMETHOD.
ENDCLASS.

START-OF-SELECTION.
  DATA status TYPE REF TO cl_status.
  status = cl_status=>approved.
  CASE status.
    WHEN cl_status=>approved.
      MESSAGE 'approved' TYPE 'I'.
    WHEN cl_status=>rejected.
      MESSAGE 'rejected' TYPE 'I'.
  ENDCASE.

From ABAP release 7.51 it is also possible to use enumerated objects in ABAP.

See also this blog for more info.

Simple example:

TYPES:
  BEGIN OF ENUM ty_enum_status STRUCTURE status,
    approved,
    rejected,
  END OF ENUM ty_enum_status STRUCTURE status.

DATA my_status TYPE ty_enum_status.
my_status = status-approved.

Example for tables:

TYPES:
  BEGIN OF ENUM ty_enum_mealtype STRUCTURE mealtype BASE TYPE smeal-mealtype,
    unknown    VALUE IS INITIAL,
    vegetarian VALUE 'VE',
    fish       VALUE 'FI',
    flesh      VALUE 'FL',
  END OF ENUM ty_enum_mealtype STRUCTURE mealtype.

SELECT SINGLE * FROM smeal
  WHERE carrid     = 'LH'
    AND mealnumber = 1
  INTO @DATA(smeal).

" For comparing an enumerated component with a data object of the base type,
" it requires a conversion to the enumerated type
DATA(enum_mealtype) = SWITCH #( CONV ty_enum_mealtype( smeal-mealtype )
  WHEN mealtype-vegetarian THEN mealtype-fish
  WHEN mealtype-fish       THEN mealtype-flesh
  WHEN mealtype-flesh      THEN mealtype-vegetarian ).

" Conversion between ENUM type and string type - This takes the first characters 
" of the name of the enumerated component
ASSERT CONV string( enum_mealtype ) = SWITCH #( enum_mealtype
  WHEN mealtype-unknown    THEN `UNKNOWN`
  WHEN mealtype-vegetarian THEN `VEGETARIAN`
  WHEN mealtype-fish       THEN `FISH`
  WHEN mealtype-flesh      THEN `FLESH` ).

" Assigning an enumerated variable to a data object of the base type
smeal-mealtype = CONV smeal-mealtype( enum_mealtype ).

" Conversion between ENUM type and base type
ASSERT CONV smeal-mealtype( enum_mealtype ) = SWITCH #( enum_mealtype
  WHEN mealtype-unknown    THEN '  '
  WHEN mealtype-vegetarian THEN 'VE'
  WHEN mealtype-fish       THEN 'FI'
  WHEN mealtype-flesh      THEN 'FL' ).

" Use CONV for assigning an enumerated component to a data object of the base type
smeal-mealtype = CONV #( mealtype-vegetarian ).
ASSERT smeal-mealtype = 'VE'.

" If you don't use CONV, you'll get the first characters of the name of the 
" enumerated component
smeal-mealtype = mealtype-unknown.
ASSERT smeal-mealtype = 'UN'.