# extends_object/2-3

## Description

    extends_object(Prototype, Parent)
    extends_object(Prototype, Parent, Scope)

Enumerates, by backtracking, all pairs of objects such that the first one extends the second. The relation scope is represented by the atoms `public`, `protected`, and `private`.

## Modes and number of proofs

    extends_object(?object_identifier, ?object_identifier) - zero_or_more
    extends_object(?object_identifier, ?object_identifier, ?scope) - zero_or_more

## Errors

`Prototype` is neither a variable nor a valid object identifier:
`type_error(object_identifier, Prototype)`
`Parent` is neither a variable nor a valid object identifier:
`type_error(object_identifier, Parent)`
`Scope` is neither a variable nor an atom:
`type_error(atom, Scope)`
`Scope` is an atom but an invalid entity scope:
`domain_error(scope, Scope)`

## Examples

    % enumerate objects derived from the state_space prototype:
    | ?- extends_object(Object, state_space).

    % enumerate objects publicly derived from the list prototype:
    | ?- extends_object(Object, list, public).

See also

current_object/1, instantiates_class/2-3, specializes_class/2-3