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Swift 2 Design Patterns
Swift 2 Design Patterns

Swift 2 Design Patterns: Build robust and scalable iOS and Mac OS X game applications

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Swift 2 Design Patterns

Chapter 2. Structural Patterns – Decorator, Proxy, and Bridge

After reviewing the five creational patterns in the previous chapter, we will now talk about another category of patterns: the structural patterns. There are seven patterns to talk about; these patterns ease the design by identifying a simple way to realize relationships between entities.

We will see how these patterns help you to encapsulate the composition of objects through the use of an interface, allowing you to conveniently abstract your system as the creational pattern does to encapsulate the creation of objects. Structural patterns highlight the use of interfaces.

You will see how the composition is designed; we will not interfere with the object itself but with the one that will transfer the structuration. This second object is strongly related to the first one. Indeed, the first object presents the interface to the client and manages its relationship with the second object, which, manages the composition...

Static and dynamic composition

We can have several possible implementations. The classic way to design this is to differentiate these implementations in subclasses. In this case, we will provide an interface from where our classes will implement this interface.

This solution consists of a static composition. Indeed, once the implementation class of an object is chosen, we can no longer change it. The following diagram is the implementation of an object by heritage:

Static and dynamic composition

Another way is to separate the implementation in another object. The implementation parts are managed by an instance of the ConcreteImplementationA class or by the ConcreteImplementationB class. This reference is referred by the implementation attribute. This instance can then be easily substituted by another instance at runtime. This composition is dynamic.

The following UML class diagram shows us clearly how to structure your objects using a dynamic composition. The ConcreteImplementation class can be switched at runtime, without...

The decorator pattern

The first structural pattern that we will discuss is the decorator pattern. It introduces you to the object substitution by adding new functionalities or behaviors.

Roles

The main objective of this pattern is to dynamically add new functionalities to an object. The interface of the object will not be modified, so from the client's perspective, this is fully transparent.

This pattern is an alternative to the addition of a subclass that adds functionalities to its parent class. A key implementation point in the decorator pattern is that decorators both inherit the original class and contain an instantiation of it.

This pattern can be used when:

  • A system adds dynamically new functionalities to an object, without having to modify its interface, which means without having to modify the client of this object
  • A system manages the behavior that can be dynamically removed
  • The use of inheritance is not a good option because of an already complex class hierarchy

Design

The generic...

The proxy pattern

The second pattern that we will talk about in this chapter is the proxy pattern. It is often used for security or optimization purposes.

Roles

The objective of the proxy pattern is to substitute an object (the subject) with another one that will control its access. The object that substitutes the subject shares the same interface, so it is transparent from the consumer's perspective. The proxy is often a small (public) object that stands in for a more complex (private) object that is activated once certain circumstances are clear. The proxy adds a level of indirection by accepting requests from a client object and passing them to the real subject as necessary.

The proxy pattern is used in object-oriented programming. There are several types of proxies, which are as follows:

  • A virtual proxy: This allows you to create a "big" object at the appropriate time (used when the creation process is slow)
  • A remote proxy: This allows you to access an object that is available...

The bridge pattern

Remember that, at the beginning of the chapter, we discussed dynamic composition that allows you to change the implementation of an object at runtime. The bridge pattern is another structural pattern that allows this.

Roles

The bridge pattern decouples an abstraction from its implementation. This means that this pattern separates the implementation of an object from its representation and interface.

Thus, firstly, the implementation can fully be encapsulated, and secondly, the implementation and representation can independently change, without having any constraints between them.

This pattern can be used:

  • To avoid a strong link between the object representation and its implementations
  • To avoid any impact between the interaction of the objects and their clients when the implementations of objects are modified
  • To allow the representation of objects and their implementations to keep their extension capability by creating new subclasses
  • To avoid to obtain very complex classes hierarchies...

Summary

We discussed the three structural patterns in this chapter: the decorator pattern, the proxy pattern, and the bridge pattern. From a high-level perspective, all of them help you extend classes without using inheritance, but using a dynamic composition of its class hierarchy.

Extending our original class has some impact on our original object except for the proxy pattern where it remains completely unchanged. The decorator pattern that needs to be designed needs to have the original class already developed because every concrete decorator needs to implement an interface based on the original object structure. The bridge pattern is more closely coupled, and there is an understanding that the original object must incorporate considerable references to the rest of the system.

We also discussed all the patterns that rely on rerouting operations. We learned that the rerouting is always done from the new code back to the original.

It is important to note that in real-time applications, where...

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Description

Swift is a multi-paradigm language. It has expressive features familiar to those used to work with modern functional languages, while also keeping the object-oriented features of Objective-C. It remains compatible with Apple’s legacy codes and frameworks. A design pattern systematically names, motivates, and explains a general design that addresses a recurring design problem in object-oriented systems. It describes the problem, the solution, when to apply the solution, and its consequences. It also gives implementation hints and examples. Knowledge about design patterns is also one of the best ways to make you different compared to other low-level developers. This book shows you how to use Swift 2 to learn about 23 Gang of Four (GoF) design patterns, and is organized into three categories. The book will present you the five creational patterns, followed by the seven structural patterns, and finishing with the 11 behavioral patterns as defined by the GoF. Each chapter will introduce the pattern by defining its role, which common problems the pattern should be used for, its generic UML representation, how each objects presented in the class diagram participate in the pattern, and what the role of each of these objects is. The book then presents you with a concrete case as an illustration that will be used to implement the pattern using Swift.

Who is this book for?

This book is intended for competent Swift developers who want to apply enduring design patterns with Swift to structure and scale their application code.
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Length: 224 pages
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Table of Contents

9 Chapters
1. Creational Patterns Chevron down icon Chevron up icon
2. Structural Patterns – Decorator, Proxy, and Bridge Chevron down icon Chevron up icon
3. Structural Patterns – Composite and Flyweight Chevron down icon Chevron up icon
4. Structural Patterns – Adapter and Facade Chevron down icon Chevron up icon
5. Behavioral Patterns – Strategy, State, and Template Method Chevron down icon Chevron up icon
6. Behavioral Patterns – Chain of Responsibility and Command Chevron down icon Chevron up icon
7. Behavioral Patterns – Iterator, Mediator, and Observer Chevron down icon Chevron up icon
8. Behavioral Patterns – Visitor, Interpreter, and Memento Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

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Nasser Nov 17, 2015
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This book helped me to my current project . It is very clear . I recommend it .
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This book verges on the surreal in its awfulness. It reads like a 1982 VCR manual translated from Japanese into English by a native speaker of Italian. Truly - nearly every paragraph has some terrible linguistic convolution stunning in its cluelessness. Imagine 2001's HAL, had he been an autistic child. The author thinks nothing of beginning any number of successive sentences with the same words and seems to regard all articles and conjunctions as interchangeable. Misspellings, typos, syntax & tense errors, and word misusage all abound. The result is a droning, bizarrely robotic glossolalia overflowing with numbing repetition punctuated by strange quirks and distractions, all of which achieves the goal of rendering an already esoteric subject opaque.Nor does the ugliness stop there. The ebook includes delights such as entire pages with a single sentence and other layout disasters that suggest a computer generated text untouched by any human being. Vast expanses of white space interrupt the text; perhaps half the pages are more than half blank. It appears to be a draft website or classroom presentation dumped to text. Printed, there'd be enough room to write an entirely new (and one hopes, better) text in the white space provided.Perhaps the author is a non-native speaker of English, but that in no way excuses the publisher for releasing this half-baked abortion. One can only assume Packt employs no editors and vetted this shameful mess not at all.
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