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.. This file is part of Logtalk https://logtalk.org/ 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. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
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.. rst-class:: align-right
built-in predicate
.. index:: pair: create_category/4; Built-in predicate .. _predicates_create_category_4:
::
create_category(Identifier, Relations, Directives, Clauses)
Creates a new, dynamic category. This predicate is often used as a primitive to implement high-level category creation methods.
Note that, when opting for runtime generated category 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 category in long-running applications, is to recycle, whenever possible, the identifiers.
When creating a new dynamic parametric category, access to the object
parameters must use the :ref:methods_parameter_2
built-in execution
context method.
When using Logtalk multi-threading features, predicates calling this built-in predicate may need to be declared synchronized in order to avoid race conditions.
::
create_category(?category_identifier, @list(category_relation)
, @list(category_directive)
, @list(clause)
) - one
| Relations
, Directives
, or Clauses
is a variable:
| instantiation_error
| Identifier
is neither a variable nor a valid category identifier:
| type_error(category_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, implements/1)
| permission_error(repeat, entity_relation, extends/1)
| permission_error(repeat, entity_relation, complements/1)
| Directives
is neither a variable nor a proper list:
| type_error(list, Directives)
| Clauses
is neither a variable nor a proper list:
| type_error(list, Clauses)
::
| ?- create_category(
tolerances,
[implements(comparing)],
[],
[epsilon(1e-15), (equal(X, Y) :- epsilon(E), abs(X-Y) =< E)]
)
.
.. seealso::
:ref:predicates_abolish_category_1
, :ref:predicates_category_property_2
,
:ref:predicates_current_category_1
,
:ref:predicates_complements_object_2
, :ref:predicates_extends_category_2_3
,
:ref:predicates_imports_category_2_3