anyclass

anyclass

the ancestor of all classes

Syntax   anyclass

Description   There is a predefined class called anyclass, which is the root of the expansion tree. All classes that do not have inherit lists are considered to be expansions of anyclass. The main purpose of anyclass is to allow pointers that can locate objects of any class.

Example   Here is the declaration of a pointer p that can locate an object of any class.

var p : pointer to anyclass % Short form: var p : ^ anyclass var q : pointer to stack % Short form: var q : ^ stack new q % Create a stack object p := q % Legal because p's class % is an ancestor of q's class
Assuming stack is a class, this creates a stack object and places its location in q and p. The compiler will not allow a call to stack's exported subprograms using p directly, as in:

p -> push (14) % ILLEGAL! anyclass has no operations
An assignment from p to q is legal, as in:

q := p % Checks that p locates a stack object (or descendant)
This implies a run time check to make sure that p locates an object that is a stack (or a descendant of a stack).
Here is a way to call a subprogram exported from stack using p:

stack (p) . push (14) % Checks that p locates a stack object
This checks to see that p locates a stack object (or a descendant) before calling the stack operation push.

Details   It is legal to create objects of the class called anyclass, but this is not of much use, because there is nothing you can do with these objects (they have no operations). It is legal to assign these objects to other objects of the same class (anyclass), although this accomplishes nothing.

See also   objectclass, which takes a class pointer and produces the class of the object located by the pointer. This is used for testing to determine the class of the object located by a pointer.
See also class. See also export list, import list, inherit list, implement list and implement by list.

Syntax	anyclass
Description	There is a predefined class called anyclass, which is the root of the expansion tree. All classes that do not have inherit lists are considered to be expansions of anyclass. The main purpose of anyclass is to allow pointers that can locate objects of any class.
Example	Here is the declaration of a pointer p that can locate an object of any class. `var p : pointer to anyclass % Short form: var p : ^ anyclass var q : pointer to stack % Short form: var q : ^ stack new q % Create a stack object p := q % Legal because p's class % is an ancestor of q's class` Assuming stack is a class, this creates a stack object and places its location in q and p. The compiler will not allow a call to stack's exported subprograms using p directly, as in: `p -> push (14) % ILLEGAL! anyclass has no operations` An assignment from p to q is legal, as in: `q := p % Checks that p locates a stack object (or descendant)` This implies a run time check to make sure that p locates an object that is a stack (or a descendant of a stack). Here is a way to call a subprogram exported from stack using p: `stack (p) . push (14) % Checks that p locates a stack object` This checks to see that p locates a stack object (or a descendant) before calling the stack operation push.
Details	It is legal to create objects of the class called anyclass, but this is not of much use, because there is nothing you can do with these objects (they have no operations). It is legal to assign these objects to other objects of the same class (anyclass), although this accomplishes nothing.
See also	objectclass, which takes a class pointer and produces the class of the object located by the pointer. This is used for testing to determine the class of the object located by a pointer. See also class. See also export list, import list, inherit list, implement list and implement by list.