.. 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

directive

.. index:: pair: initialization/1; Directive .. _directives_initialization_1:

initialization/1

Description

::

initialization(Goal)

When used within an object, this directive defines a goal to be called after the object has been successfully loaded into memory. When used at a global level within a source file, this directive defines a goal to be called after the source file is successfully compiled and loaded into memory.

The loading context can be accessed from this directive by calling the :ref:predicates_logtalk_load_context_2 predicate. Note that the usable loading context keys depend on the directive scope (file or object).

Multiple initialization directives can be used in a source file or in an object. Their goals will be called in the same order as the directives at loading time.

.. note::

Arbitrary goals cannot be used as directives in source files. Any goal that should be automatically called when a source file is loaded must be wrapped using this directive.

Categories and protocols cannot contain initialization/1 directives as the initialization goals would lack a complete :term:`execution context <predicate execution context>` that is only available for objects.

Although technically a global initialization/1 directive in a source file is a Prolog directive, calls to Logtalk built-in predicates from it are usually compiled to improve portability, improve performance, and provide better support for embedded applications.

.. warning::

Some backend Prolog compilers declare the atom initialization as an operator for a lighter syntax. But this makes the code non-portable and is therefore a practice best avoided.

Template and modes

::

initialization(@callable)

Examples

::

% call the init/0 predicate after loading the % source file containing the directive

:- initialization(init).

::

% print a debug message after loading a % source file defining an object

:- object(log).

:- initialization(start_date).

start_date :-
    os::date_time(Year, Month, Day, _, _, _, _),
    logtalk::print_message(debug, my_app, 'Starting date: ~d-~d-~d~n'+[Year,Month,Day]).

:- end_object.

.. seealso::

:ref:predicates_logtalk_load_context_2