Design Pattern Examples

Created by Stephen P. Lepisto

Copyright (C) 2023 by Stephen P. Lepisto. All rights reserved.

Overview

This reference material is a treatise on the patterns defined in the book, Design Patterns: Elements of Object-Oriented Software, by Gamma, Helm, Johnson, and Vlissides.

These patterns appeared over and over in the many years that object-oriented programming grew and matured. In 1995, Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides formalized 23 patterns into a book, the first of its kind.

To be sure, these patterns existed before the Design Patterns book was written, which is why the Gang of Four wrote the book. It was an attempt to formalize the most well-known patterns, to provide terminology, methodology, and a place to start discussions on the discipline of creating software, while focusing on the latest movement (at that time) of object-oriented programming. However, most of the design patterns in the book are not limited to object-oriented design or even programming languages that prominently focus on object-oriented features.

This documentation is built from my efforts to implement most of the design patterns in four different programming languages: C, C++, C#, and Python. I also converted the patterns to Rust, but since Doxygen does not know how to parse Rust (as of July 6, 2023), I have captured the Rust source code and documentation in a separate location: Rust Design Pattern Examples.

Source Code

The source code for these examples can be found on GitHub: https://github.com/stephenlepisto/designpatternexamples.

Although this documentation provides overviews of each pattern and some links into the code, reading the code at length is where the real learning begins. I encourage you to download the code and browse, dive deep to follow what piques your interest. Where feasible, I have attempted to adhere to the idioms of each language but I also tried to maintain similar naming styles across all versions to make it easier to compare implementations.

Explore. Educate yourself. Enjoy!

The Design Pattern Examples Implemented Here

• Adapter Pattern
• Bridge Pattern
• Command Pattern
• Composite Pattern
• Decorator Pattern
• Facade Pattern
• Flyweight Pattern
• HandlerChain Pattern
• Interpreter Pattern
• Iterator Pattern
• Mediator Pattern
• Memento Pattern
• Null Object Pattern
• Observer Pattern
• Proxy Pattern
• State Pattern
• Strategy Pattern
• Visitor Pattern

The Design Patterns with Indirect Examples

These design patterns do not have dedicated examples but instead point to one or more of the above examples that use the following patterns.

• Factory Pattern
• Private Class Data Pattern
• Singleton Pattern

The Design Patterns with No Examples

I did not create examples of the following design patterns as they are intended for highly complex, object-oriented designs. I tend to keep away from such complex designs as they represent, in my opinion, the worst excesses of object-oriented programming that lead to the problems of being very hard to learn, very hard to debug, and therefore, very hard to maintain.

• Abstract Factory Pattern
• Builder Pattern
• Prototype Pattern
• Template Pattern