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


The singleton pattern was part of the original Design Patterns collection. It makes sure that a class, which we call a singleton class, has only one instance. In other words, only one object of that class may ever be created during the program's life. Such a class must also provide global access to this instance.


Let me give a real-life example to clarify this definition. You probably live in a country that allows one, and only one, president (or monarch, head of state, and so on.) to exist at the same time. So, that person is a singleton.

You will notice that the pattern tells us nothing about how that one singleton instance should be destroyed. It also doesn't specify when the singleton instance should be created.

Whenever you need to create a singleton, you should first answer the following questions:

  • Does the singleton have to be initialized on demand, or will it be created on first use?
  • Can the singleton be destroyed when the program ends, or should it disappear when nobody...