SAP CASTING - Guide

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Casting

ABAP_BACKGROUND
Casting refers to the process of handling a data object by assuming a certain data type. This definition is different to the meaning of the concept in other programming languages, such as Java. Here, casting means a different concept which is referred to as 'conversion' in ABAP. Casting in ABAP is either explicit or implicit:

Explicit casting is possible by using the CASTING addition with the ASSIGN statement and by using the ASSIGNING addition in statements for processing internal tables. Assignments between reference variables allow upcasts and downcasts. Obsolete explicit casting is also possible for formal parameters and field symbols, if the STRUCTURE addition is used.

Implicit casting is sometimes performed for special assignments or during operand handling at certain operand positions. A common example is the handling of flat structures using character-like-only components as a single field of type c.

ABAP_RULE
Avoid implicit casting
Avoid implicit casting. If a cast to another data type is required, it can usually be implemented explicitly using ASSIGN ... CASTING.

ABAP_DETAILS
Implicit casting can potentially occur if structures are used as follows:

Assignments between incompatible structures or structures and elementary data objects

Comparisons between structures and elementary data objects

Using structures in operand positions where elementary data objects are expected

Reads from the database using SELECT * ... INTO wa

Using the INCREMENT addition for the ASSIGN statement
The use of implicit casting is prone to errors and produces source code that is difficult to understand. If the CASTING addition is used when handling field symbols, explicit casting can be implemented, which is easier to follow and understand. The explicit casting option is a very important reason to use field symbols.

ABAP_EXAMPLE_BAD
The following source code shows the assignment of a text string to a structure with only character-like components. An implicit casting occurs here, which is regarded as unwanted according to the above rule. The entire structure is handled as a text field of type c and length 6. TYPES: BEGIN OF structure,
comp1 TYPE c LENGTH 2,
comp2 TYPE c LENGTH 4,
END OF structure.
DATA structure TYPE structure.
DATA text TYPE string.
...
text = ...
structure = text.
ABAP_EXAMPLE_END

ABAP_EXAMPLE_GOOD
The following source code improves the example above, by assigning the structure to a field symbol of type c. Explicit casting occurs. Only the character-like field symbol is used to handle the structure as a character-like field. ...
FIELD-SYMBOLS < text> TYPE c.
...
ASSIGN structure TO < text> CASTING.
< text> = ...
ABAP_EXAMPLE_END