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.. rst-class:: align-right

built-in predicate

.. index:: pair: create_object/4; Built-in predicate .. _predicates_create_object_4:

create_object/4

Description

::

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.

Modes and number of proofs

::

create_object(?object_identifier, @list(object_relation), @list(object_directive), @list(clause)) - one

Errors

| 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)

Examples

::

% 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