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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/4

Description

::

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.

Modes and number of proofs

::

create_category(?category_identifier, @list(category_relation), @list(category_directive), @list(clause)) - one

Errors

| 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)

Examples

::

| ?- 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