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ABENCLASS_COMPONENTS_ADDRESSING - CLASS COMPONENTS ADDRESSING

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- Accessing Class Components

When accessing class components, there is a difference between access from inside and outside of the same class. In internal access, that is, within a method of the same class, the name of the component is sufficient. In external access, the object, in the case of instance components, and the class, in the case of static components, must be specified using an object component selector or class component selector. Here, a distinction can be made between static and dynamic variants.

For static access, object reference variables can only be used to access components that are known to the reference variable. These are the components that are available in the static type of the reference variable (class or interface). Class reference variables that are typed with reference to a superclass but point to subclasses know only the superclass components and the interface references know only interface components.

With dynamic access, the dynamic type is used to determine the component for class reference variables. This is the type of the object to which the reference refers, and not the type used for typing the reference. For interface reference variables the static type is also used for dynamic access, that is, the type that was used to type the reference.

This means that in dynamic access, reference variables that are typed with reference to a superclass and that point to subclasses can be used to access any component of the subclass for which dynamic access is possible. In particular, reference variables of the type REF TO OBJECT can be used to access components dynamically. Dynamic access does not allow interface reference variables to be used to access class-specific components and only the corresponding interface components can be accessed. It is not possible to access class-specific components using interface reference variables because the prefix intf~ is always used implicitly when interface reference variables are used.

Static Access

The following syntax applies (oref is an object reference variable):

• Access to an instance attribute attr: oref->attr

• Call of an instance method meth: oref->meth( ... )

In addition to reference variables, the class name can be used to access static components :

• Access to a static attribute attr: class=>attr

• Call of a static method meth: class=>meth( ... )

In this context, it is important to note that the properties of instance attributes behave like static components. Therefore, in a LIKE addition, the class component selector or reference variables can be used to refer to the visible attributes of a class, without first creating an object.

Apart from specifying the name directly, the self-reference me can also be used within a class to access its components:

• Access to personal attributes attr within the class: me->attr

• Call of a personal method meth within the same class: me->meth( ... )

The self-reference allows an object to pass a reference to itself to other objects. In addition, attributes within an object which are hidden by the local attributes of the method can be accessed using methods.

Within a redefined method of a subclass, the pseudo reference super can be used to access the hidden method in one of the superclasses:

• Call of an hidden method meth: super->meth( ... )

Within the instance constructor of a subclass, the pseudo reference super must be used to call the instance constructor of the direct superclass:

• Call of the constructor of the direct superclass:

super->constructor( ... )

As a special method for accessing attributes, the attributes for key access to internal tables can be used if they contain reference variables.

Dynamic Access

Dynamic access to class components is possible for attributes (dynamic access) and for method calls (dynamic invoke).

Accessing Attributes Dynamically

Dynamic access to attributes is possible using dynamic ASSIGN statements on field symbols.

The following variants can be used (oref is an object reference variable):

• Completely dynamic specification:

ASSIGN (f) TO <fs>.

• Partly dynamic specification for instance attributes:

ASSIGN oref->(f) TO <fs>.

• Partly dynamic specification for static attributes:

ASSIGN (f1)=>(f2) TO <fs>.

The content of the fields f, f1 and f2 is interpreted as descriptors of attributes. In a completely dynamic case, f can, for example, have the content 'oref->attr'. In the case of the partly dynamic specification for instance attributes, f only describes the attribute (which itself can in turn describe another attribute). f1 and f2 can be class names and static attributes.

Dynamic Method Calls

The following syntax applies (oref is an object reference variable):

• Call of an instance method meth:

CALL METHOD oref->(f)

• Call of a static method meth:

CALL METHOD class=>(f)

CALL METHOD (c)=>meth

CALL METHOD (c)=>(f)

• Call of a method meth within the same class:

CALL METHOD (f)

CALL METHOD me->(f)

f and c are fields that contain the name of the method meth or class class.

In the case of a dynamic method call, the actual parameter can be passed dynamically to specific internal tables, similarly to calling function modules.

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