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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
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
.. rst-class:: align-right
built-in predicate
.. index:: pair: create_object/4; Built-in predicate .. _predicates_create_object_4:
::
create_object(Identifier, Relations, Directives, Clauses)
Creates a new, dynamic object. The word :term:object
is used here
as a generic term. This predicate can be used to create new prototypes,
instances, and classes. This predicate is often used as a primitive to
implement high-level object creation methods.
Note that, when opting for runtime generated object 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 objects in long-running applications, is to recycle, whenever possible, the identifiers.
When creating a new dynamic parametric object, access to the object parameters
must use the :ref:methods_parameter_2
built-in execution context method.
Declared predicates (using scope clauses in the Directives
argument)
are implicitly declared also as dynamic.
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_object(?object_identifier, @list(object_relation)
, @list(object_directive)
, @list(clause)
) - one
| Relations
, Directives
, or Clauses
is a variable:
| instantiation_error
| Identifier
is neither a variable nor a valid object identifier:
| type_error(object_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, imports/1)
| permission_error(repeat, entity_relation, extends/1)
| permission_error(repeat, entity_relation, instantiates/1)
| permission_error(repeat, entity_relation, specializes/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 a stand-alone object (a prototype):
| ?- create_object(
translator,
[],
[public(int/2)],
[int(0, zero)]
)
.
% create a prototype derived from a parent prototype:
| ?- create_object(
mickey,
[extends(mouse)],
[public(alias/1)],
[alias(mortimer)]
)
.
% create a class instance:
| ?- create_object(
p1,
[instantiates(person)],
[],
[name('Paulo Moura'), age(42)]
)
.
% create a subclass:
| ?- create_object(
hovercraft,
[specializes(vehicle)],
[public([propeller/2, fan/2])],
[]
)
.
% create an object with an initialization goal:
| ?- create_object(
runner,
[instantiates(runners)
],
[initialization(::start)],
[length(22)
, time(60)
]
).
% create an object supporting dynamic predicate declarations:
| ?- create_object(
database,
[],
[set_logtalk_flag(dynamic_declarations, allow)],
[]
)
.
.. seealso::
:ref:predicates_abolish_object_1
,
:ref:predicates_current_object_1
,
:ref:predicates_object_property_2
,
:ref:predicates_extends_object_2_3
,
:ref:predicates_instantiates_class_2_3
,
:ref:predicates_specializes_class_2_3
,
:ref:predicates_complements_object_2