| anyclass | the ancestor of all classes |
| Syntax | anyclass
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| 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.
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| 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 operationsAn 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 objectThis checks to see that p locates a stack object (or a descendant) before calling the stack operation push.
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| 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.
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| 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.
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