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 last pattern in this chapter, mementohelps us save and restore a state of a complex object. It was originally introduced by the Gang of Four.

When you want to store and restore a current state of a complex object, you can easily run into problems with encapsulation. There may, for example, exist an internal state that is important for the correct functioning of the object, but is not accessible to the public. In such a case, we may not be able to access this state from the code that is not part of the object.

Even if all internal fields are accessible by the public, accessing internal state from external code is a bad practice. The internal representation of an object may change unexpectedly (for example, with a software update), and if a maintainer of such external code is not aware of that, the program would break.

The memento pattern prescribes how a complex object (called originator) saves its internal state into a simpler object (memento). An external object (caretaker) can...