---

jupyter: jupytext: text_representation: extension: .md format_name: markdown format_version: '1.3' jupytext_version: 1.16.7 kernelspec: display_name: Logtalk language: logtalk name: logtalk_kernel ---

<!--

This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2025 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. -->

patching

This folder contains an example that shows how to use a complementing category to patch broken object predicate declarations and definitions (without modifying its source code), thus providing functionality similar to Objective-C categories.

The complemented objects must be compiled with the flag complements set to allow (its default value is usually deny). This solution was adapted to improve performance of applications that don't make use complementing categories and to provide a solution for preventing the use of categories to break object encapsulation. Note that the complements flag can be set on a per-object basis by using the set_logtalk_flag/2 directive.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the example:

logtalk_load(patching(loader)).

<!-- true. -->

Find categories that complement objects:

complements_object(Category, Object).

<!-- Category = patch, Object = broken. -->

Verify the patch in the patch category for the predicate is_proper_list/1 defined in the object broken:

broken::is_proper_list([1,2,3]).

<!-- true. -->

broken::is_proper_list(_).

<!-- false. -->

broken::is_proper_list([a,b,c|_]).

<!-- false. -->

Verify the patch in the patch category for the wrong scope of the last/3 predicate declared in the object broken:

broken::last(_, _, _).

<!-- permission_error(access, private_predicate, last/3), broken::last(_, _, _), user -->

Verify the patch in the patch category for the wrong scope of the last/3 predicate declared in the object broken:

broken::nextto(2, 3, [1,2,3]).

<!-- true. -->