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References References are pointers to instances. Pointers to data objects are data references>. Pointers to instances of classes are object references>. References occur in ABAP as the content of reference variables. Reference variables are data objects whose data type is a reference type. Reference types are always created using the addition REF TO>>. The content of reference variables can be checked using the predicate expression IS BOUND>>. The reference type is the static type of a reference variable. It defines to which types of instances its references can point. The dynamic type of a reference variable is the type from which an object was instantiated to which a reference variable points. The static type is always more general than or the same as the dynamic type. A dynamic type can be a data type or a class. A reference type or static type can be a type for a data reference variable> or an object reference variable>. The latter are subdivided into class reference variables> and interface reference variables>. Special conversion rules> apply to assignments between reference variables, depending on the static type. These rules ensure that the dynamic type is never more general than the static type (upcast>, downcast>). Depending on where the object referenced by a reference variable is stored, memory-preserving heap references > or non-memory-preserving stack references> can be distinguished. Special weak references> that are represented by objects of a system class, do not keep an object alive.
Data references>
Object references>
Heap references and stack references>
Weak references> A reference in a reference variable is valid if it points to an object. For this, the predicate expression IS BOUND >> is true. A non-initial reference can be invalid if it points to deleted objects. A heap reference> that points to a line in an internal table can become invalid if the line is deleted. A stack reference> can become invalid if the referenced data object is removed from the stack.
Latest notes:
From a technical perspective, a reference in ABAP does not refer directly to an object but to a header instead, which contains the address of the actual object and other administrative information. See also Memory Management of Deep Data Objects>.
Internally, strings>, internal tables>, and boxed components> are also addressed using references, which do not appear as the content of reference variables. NON_V5_HINTS ABAP_HINT_END