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Data Type for Truth Values
ABAP_BACKGROUND Truth values are results of logical expressions. A truth value is either true or false. ABAP does not yet support Boolean data types and thus does not support data objects for truth values. Therefore, the result of a logical expression cannot be assigned directly to a data object. It has become common practice to express the truth value true as value X and the truth value false as a blank. There are also Boolean functions that have a logical expression as an argument and are returned as the value X or a blank, depending on the result. To make it easier to handle truth values expressed in this way, there is a predefined data element ABAP_BOOLEAN of data type CHAR of length 1 and the type pool abap contains constants abap_true of value X and abap_false of value blank as substitutes for a real Boolean data type. There is also a constant abap_undefined of value -.
ABAP_RULE Use the data type ABAP_BOOLEAN for truth values When working explicitly with truth values, use the data element ABAP_BOOLEAN as a substitute for a real Boolean data type. A data object declared in this way should have no values other than the predefined constants abap_true and abap_false (also abap_undefined) from type pool ABAP.
ABAP_DETAILS Using the type ABAP_BOOLEAN and the constants abap_true and abap_false makes it clear that truth values are being used here. In accordance with the rule for avoiding literals in operand positions, not only the literals 'X' and ' ' should be used. State queries about the predicate operators IS INITIAL and IS NOT INITIAL or the use of the constant space are also not advisable, because they require knowledge of the technical values of abap_true and abap_false, which are not significant in the sense of real Boolean data objects. The type pool abap contains a third constant for the type ABAP_BOOLEAN, namely abap_undefined. However, implementing a three-value logic is only useful and recommended in exceptional cases. In this case, note that abap_undefined does not contain the initial value for a variable of type ABAP_BOOLEAN. The initial value is always the value of abap_false. However, the value of abap_undefined can, if required, be specified using the addition VALUE when declaring a truth value as the start value.
Latest notes: The type pool abap also contains a data type abap_bool as a predecessor of data element ABAP_BOOLEAN. It is recommended that the data element ABAP_BOOLEAN is used in new programs because it is more versatile. As a data element it can be also used in ABAP Dictionary objects or in ABAP CDS. A data type from type pool ABAP can be used in ABAP programs only. ABAP_HINT_END
ABAP_EXAMPLE_BAD The following source code shows an unsuitable emulation of the Boolean data objects not present in ABAP. DATA is_found TYPE c LENGTH 1. ... is_found = 'X'. ... IF is_found IS NOT INITIAL. ... ENDIF. ABAP_EXAMPLE_END
ABAP_EXAMPLE_GOOD The following source code shows the recommended emulation of the Boolean data objects not present in ABAP. DATA is_found TYPE abap_boolean. ... is_found = abap_true. ... IF is_found = abap_true. ... ENDIF. ABAP_EXAMPLE_END
