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   SPDX-FileCopyrightText: 1998-2024 Paulo Moura <pmoura@logtalk.org>
   SPDX-License-Identifier: Apache-2.0

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
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.. rst-class:: align-right

**built-in predicate**

.. index:: pair: extends_category/2-3; Built-in predicate
.. _predicates_extends_category_2_3:

``extends_category/2-3``
========================

Description
-----------

::

   extends_category(Category, ParentCategory)
   extends_category(Category, ParentCategory, Scope)

Enumerates, by backtracking, all pairs of categories 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_category(?category_identifier, ?category_identifier) - zero_or_more
   extends_category(?category_identifier, ?category_identifier, ?scope) - zero_or_more

Errors
------

| ``Category`` is neither a variable nor a valid protocol identifier:
|     ``type_error(category_identifier, Category)``
| ``ParentCategory`` is neither a variable nor a valid protocol identifier:
|     ``type_error(category_identifier, ParentCategory)``
| ``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 the categories extended by the derailleur category:
   | ?- extends_category(derailleur, Category).

   % enumerate categories that privately extend the basics category:
   | ?- extends_category(Category, basics, private).

.. seealso::

   :ref:`predicates_current_category_1`,
   :ref:`predicates_complements_object_2`,
   :ref:`predicates_imports_category_2_3`
