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02_Structures.md
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@@ -10,6 +10,8 @@
- [Creating Structures](#creating-structures)
- [Creating Structures Using Existing Structured Types](#creating-structures-using-existing-structured-types)
- [Creating Structures by Inline Declaration](#creating-structures-by-inline-declaration)
- [Creating Constant and Immutable Structures](#creating-constant-and-immutable-structures)
- [Creating Enumerated Structures](#creating-enumerated-structures)
- [Creating Anonymous Structures](#creating-anonymous-structures)
- [Variants of Structures](#variants-of-structures)
- [Accessing (Components of) Structures](#accessing-components-of-structures)
@@ -251,6 +253,67 @@ LOOP AT itab INTO DATA(wa_2).
ENDLOOP.
```
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Creating Constant and Immutable Structures
- Constant structures can be created with the `... BEGIN OF ... END OF ...` additions. Their values cannot be changed.
- As shown above, the [`FINAL`](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenfinal_inline.htm) declaration operator is used to create [immutable variables](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenimmutable_variable_glosry.htm).
```abap
CONSTANTS: BEGIN OF const_struct,
num TYPE i VALUE 123,
str TYPE string VALUE `ABAP`,
n3 TYPE n LENGTH 3 VALUE '000',
c5 TYPE c LENGTH 5 VALUE 'abcde',
END OF const_struct.
DATA(num) = const_struct-num.
"const_struct-num = 456.
TYPES struct_type LIKE const_struct.
FINAL(final_struct) = VALUE struct_type( num = 987 str = `hello` n3 = '123' c5 = 'xyz' ).
DATA(num_from_final) = final_struct-num.
"final_struct-num = 1.
SELECT * FROM zdemo_abap_carr INTO TABLE @DATA(itab).
"The work area is specified as immutable variable. The variable's content cannot be changed
"in the loop, however, the variable is exchanged with the next loop pass.
LOOP AT itab INTO FINAL(wa).
DATA(carrid) = wa-carrid.
"wa-carrid = 'XY'.
ENDLOOP.
```
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Creating Enumerated Structures
Find more information on [enumerated types](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenenum_type_glosry.htm) in the [Data Types and Data Objects](16_Data_Types_and_Objects.md#abap-enumerated-types-and-objects) cheat sheet.
```abap
"When creating enumerated types, an enumerated structure can optionally be declared in
"the context of the type declaration.
"A component of an enumerated structure: An enumerated constant that exists as a component
"of a constant structure, not as a single data object.
TYPES basetype TYPE i.
TYPES: BEGIN OF ENUM t_enum_struc STRUCTURE en_struc BASE TYPE basetype,
a VALUE IS INITIAL,
b VALUE 1,
c VALUE 2,
d VALUE 3,
END OF ENUM t_enum_struc STRUCTURE en_struc.
DATA(enum_comp) = en_struc-b.
DATA(conv_enum_comp) = CONV basetype( en_struc-b ).
ASSERT conv_enum_comp = 1.
```
<p align="right"><a href="#top">⬆️ back to top</a></p>
### Creating Anonymous Structures
Using the instance operator [`NEW`](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenconstructor_expression_new.htm) and [`CREATE DATA`](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abapcreate_data.htm) statements, you can create [anonymous data objects](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenanonymous_data_object_glosry.htm "Glossary Entry"), such as anonymous structures.