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   Copyright 1998-2021 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: create_protocol/3; Built-in predicate
.. _predicates_create_protocol_3:

``create_protocol/3``
=====================

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

::

   create_protocol(Identifier, Relations, Directives)

Creates a new, dynamic, protocol. This predicate is often used as a
primitive to implement high-level protocol creation methods.

Note that, when opting for runtime generated protocol identifiers, it's
possible to run out of identifiers when using a :term:`backend Prolog compiler`
with bounded integer support. The portable solution, when creating a
large number of dynamic protocols in long-running applications, is to
recycle, whenever possible, the identifiers.

When using Logtalk multi-threading features, predicates calling this
built-in predicate may need to be declared synchronized in order to
avoid race conditions.

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

::

   create_protocol(?protocol_identifier, @list(protocol_relation), @list(protocol_directive)) - one

Errors
------

| Either ``Relations`` or ``Directives`` is a variable:
|     ``instantiation_error``
| ``Identifier`` is neither a variable nor a valid protocol identifier:
|     ``type_error(protocol_identifier, Identifier)``
| ``Identifier`` is already in use:
|     ``permission_error(modify, category, Identifier)``
|     ``permission_error(modify, object, Identifier)``
|     ``permission_error(modify, protocol, Identifier)``
| ``Relations`` is neither a variable nor a proper list:
|     ``type_error(list, Relations)``
| Repeated entity relation clause:
|     ``permission_error(repeat, entity_relation, extends/1)``
| ``Directives`` is neither a variable nor a proper list:
|     ``type_error(list, Directives)``

Examples
--------

::

   | ?- create_protocol(
           logging,
           [extends(monitoring)],
           [public([log_file/1, log_on/0, log_off/0])]
        ).

.. seealso::

   :ref:`predicates_abolish_protocol_1`,
   :ref:`predicates_current_protocol_1`,
   :ref:`predicates_protocol_property_2`,
   :ref:`predicates_conforms_to_protocol_2_3`,
   :ref:`predicates_extends_protocol_2_3`,
   :ref:`predicates_implements_protocol_2_3`
