---

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. -->

Design pattern: Composite

Description: "Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly."

This pattern can be used with both classes and prototypes.

In this sample implementation of the pattern, we choose to use classes and object composition (i.e., composite objects will store the identifiers of the objects that are part of the composite). In the sample queries, we create the instances dynamically at runtime but we could also have defined (some or all) of the instances statically in the source file.

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

%versions

Start by loading the design pattern sample implementation:

logtalk_load(design_patterns('structural/composite/loader')).

First, create some ellipses:

ellipse::(new(e1), new(e2), new(e3), new(e4)).

<!-- true. -->

Second, create some composite graphics:

composite_graphic::(new(cg), new(cg1), new(cg2)).

<!-- true. -->

Add to the composite graphic cg1 the ellipses e1, e2, and e3:

cg1::(add(e1), add(e2), add(e3)).

<!-- true. -->

Add to the composite graphic cg2 the ellipse e4:

cg2::add(e4).

<!-- true. -->

Add to the composite graphic cg the composite graphics cg1 and cg2:

cg::(add(cg1), add(cg2)).

<!-- true. -->

Finally, print the contents of the top-level composite graphic cg:

cg::print.

<!-- ellipse: e1 ellipse: e2 ellipse: e3 ellipse: e4

true. -->