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   Copyright 1998-2021 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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.. index:: pair: instantiates_class/2-3; Built-in predicate
.. _predicates_instantiates_class_2_3:

``instantiates_class/2-3``
==========================

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

::

   instantiates_class(Instance, Class)
   instantiates_class(Instance, Class, Scope)

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

Modes and number of proofs
--------------------------

::

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

Errors
------

| ``Instance`` is neither a variable nor a valid object identifier:
|     ``type_error(object_identifier, Instance)``
| ``Class`` is neither a variable nor a valid object identifier:
|     ``type_error(object_identifier, Class)``
| ``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
--------

::

   % check that the water_jug is an instante of state_space:
   | ?- instantiates_class(water_jug, state_space).

   % enumerate the state_space instances where the
   % instantiation relation is public:
   | ?- instantiates_class(Space, state_space, public).

.. seealso::

   :ref:`predicates_current_object_1`,
   :ref:`predicates_extends_object_2_3`,
   :ref:`predicates_specializes_class_2_3`
