..
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   Copyright 1998-2019 Paulo Moura <pmoura@logtalk.org>

   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,
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   See the License for the specific language governing permissions and
   limitations under the License.


.. index:: pair: assertz/1; Built-in method
.. _methods_assertz_1:

assertz/1
=========

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

::

   assertz(Head)
   assertz((Head:-Body))

Asserts a clause as the last one for a dynamic predicate. If the
predicate is not previously declared (using a scope directive), then a
dynamic predicate declaration is added to the object (assuming that we
are asserting locally or that the
:ref:`dynamic_declarations <flag_dynamic_declarations>` compiler flag
was set to ``allow`` when the object was created or compiled).

When the predicate indicator for ``Head`` is declared in a :ref:`directives_uses_2` or
:ref:`directives_use_module_2` directive, the clause is asserted in the referenced
object or module.

This method may be used to assert clauses for predicates that are not
declared dynamic for dynamic objects provided that the predicates are
declared in :term:`this`. This allows easy initialization of dynamically
created objects when writing constructors.

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

::

   assertz(+clause) - one

Errors
------

| Head is a variable:
|     ``instantiation_error``
| Head is a neither a variable nor a callable term:
|     ``type_error(callable, Head)``
| Body cannot be converted to a goal:
|     ``type_error(callable, Body)``
| The predicate indicator of Head, Name/Arity, is that of a private predicate:
|     ``permission_error(modify, private_predicate, Name/Arity)``
| The predicate indicator of Head, Name/Arity, is that of a protected predicate:
|     ``permission_error(modify, protected_predicate, Name/Arity)``
| The predicate indicator of Head, Name/Arity, is that of a static predicate:
|     ``permission_error(modify, static_predicate, Name/Arity)``
| The predicate indicator of Head, Name/Arity, does not match a declared predicate and the target object was created/compiled with support for dynamic declaration of predicates turned off:
|     ``permission_error(create, predicate_declaration, Name/Arity)``

Examples
--------

| To assert a clause as the last one for a local dynamic predicate or a dynamic predicate in :term:`this`:
|     ``assertz(Clause)``
| To assert a clause as the last one for any public or protected dynamic predicate in :term:`self`:
|     ``::assertz(Clause)``
| To assert a clause as the last one for any public dynamic predicate in an explicit object:
|     ``Object::assertz(Clause)``

.. seealso::

   :ref:`methods_abolish_1`,
   :ref:`methods_asserta_1`,
   :ref:`methods_clause_2`,
   :ref:`methods_retract_1`,
   :ref:`methods_retractall_1`
   :ref:`directives_dynamic_0`,
   :ref:`directives_dynamic_1`,
   :ref:`directives_uses_2`,
   :ref:`directives_use_module_2`
