objectclass

objectclass

of a pointer

Syntax   objectclass ( pointerExpn )

Description   The objectclass attribute is used to find the class of an object located by a pointer. The pointerExpn must be an expression that is a pointer to a class.

Example   See class for an example of classes and inheritance, in which a class called TextFile is inherited by a class called Device. The Device class adds a new exported procedure called ioCtl. In the present example, objectclass is used to test to make sure that the textFilePtr currently locates an object that was created as a Device (or as a descendant of Device). The notation Device(textFilePtr) converts the pointer to be a pointer to a Device so that ioCtl can be called.

var textFilePtr : ^ TextFile … if objectclass ( textFilePtr ) >= Device then % Can safely treat object as a Device Device ( textFilePtr ) . ioCtl … end if

Details   This example uses the class comparison operator >= which means "is a descendant of". See class.
You can only use objectclass in class comparisons. In particular, objectclass cannot be used to declare pointers. For example, this:

var p : ^objectclass (q)
is not allowed.

Syntax	objectclass ( pointerExpn )
Description	The objectclass attribute is used to find the class of an object located by a pointer. The pointerExpn must be an expression that is a pointer to a class.
Example	See class for an example of classes and inheritance, in which a class called TextFile is inherited by a class called Device. The Device class adds a new exported procedure called ioCtl. In the present example, objectclass is used to test to make sure that the textFilePtr currently locates an object that was created as a Device (or as a descendant of Device). The notation Device(textFilePtr) converts the pointer to be a pointer to a Device so that ioCtl can be called. `var textFilePtr : ^ TextFile … if objectclass ( textFilePtr ) >= Device then % Can safely treat object as a Device Device ( textFilePtr ) . ioCtl … end if`
Details	This example uses the class comparison operator >= which means "is a descendant of". See class. You can only use objectclass in class comparisons. In particular, objectclass cannot be used to declare pointers. For example, this: `var p : ^objectclass (q)` is not allowed.