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   Copyright 1998-2022 Paulo Moura <pmoura@logtalk.org>
   SPDX-License-Identifier: Apache-2.0

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   you may not use this file except in compliance with the License.
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.. index:: pair: extends_object/2-3; Built-in predicate
.. _predicates_extends_object_2_3:

``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).

.. seealso::

   :ref:`predicates_current_object_1`,
   :ref:`predicates_instantiates_class_2_3`,
   :ref:`predicates_specializes_class_2_3`
