Book Image

Hands-On Design Patterns with Delphi

By : Primož Gabrijelčič
Book Image

Hands-On Design Patterns with Delphi

By: Primož Gabrijelčič

Overview of this book

Design patterns have proven to be the go-to solution for many common programming scenarios. This book focuses on design patterns applied to the Delphi language. The book will provide you with insights into the language and its capabilities of a runtime library. You'll start by exploring a variety of design patterns and understanding them through real-world examples. This will entail a short explanation of the concept of design patterns and the original set of the 'Gang of Four' patterns, which will help you in structuring your designs efficiently. Next, you'll cover the most important 'anti-patterns' (essentially bad software development practices) to aid you in steering clear of problems during programming. You'll then learn about the eight most important patterns for each creational, structural, and behavioral type. After this, you'll be introduced to the concept of 'concurrency' patterns, which are design patterns specifically related to multithreading and parallel computation. These will enable you to develop and improve an interface between items and harmonize shared memories within threads. Toward the concluding chapters, you'll explore design patterns specific to program design and other categories of patterns that do not fall under the 'design' umbrella. By the end of this book, you'll be able to address common design problems encountered while developing applications and feel confident while building scalable projects.
Table of Contents (18 chapters)
Title Page
Copyright and Credits
About Packt


While design patterns are undoubtedly a useful tool, many prominent computer scientists have expressed criticism directed both at the Design Patterns: Elements of Reusable Object-Oriented Software book and at the general way patterns are used in practice.

Over the years, programmers have learned that the patterns in the GoF book really aren't as widely applicable as the authors thought. Lots of them only apply to the object-oriented world. If we try to use them with a functional language, they are largely useless. They can also be greatly simplified when used in aspect-oriented languages.

Delphi, however, is an object-oriented language, so we can reuse most of the Gang of Four observations. Still, it is important to keep in mind how patterns should be used in practice.

As a main rule, you should never use design patterns to architect the software. Design patterns tell you how to write code to solve a specific problem while software design should be done on a higher abstraction level, without referring to implementation details. Rather, you should use them to approach specific problems that you run into while programming.

The second idea that should be present in your mind at all times is that patterns are not the goal: they are just a tool. Design patterns formalize only some aspects of programming, not all of it. You should also never follow a design pattern blindly. Think about what it says, think about how it applies to your problem, and then use it wisely. Programming is a craft, not a paint by numbers book, and patterns are not a silver bullet.


If you look at the code and the pattern stands out to you, it was not implemented correctly. A good pattern will hide in the code, and only a careful observer will be able to say: Oh! I see you used a visitor pattern here. Nice. It is important to understand the concepts behind the design patterns, and not the exact names of the methods and properties that were used in an implementation you found somewhere (even if that was in the Design Patterns book).

Design patterns are a great tool for refactoring and communication. Hey, gals and guys, this part of our system is completely messed up, and we should use a publish/subscribe pattern instead, is a type of a statement that should appear more frequently in our discussions!