Design Patterns in Swift

Ch 0 Introduction

Sai Li @ Yowoo Tech. 2017/3/17

Agenda

• Prologue • What is Pattern? • OOP Recap

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• After OOP • Clean Code, OOP, Design Pattern,

Refactor, Platform Framework, Test • Future interview

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know nothingwork

What is a Pattern?

Christopher Alexander (1936 - )

Each pattern is a three-part rule, which expresses a relation between a certain context, a problem, and a solution.

Christopher Alexander (1979, p. 247)

Pattern is a solution to a problem in a context

• Context: A CEO of a company

• Problem: tough competition among the delivery services, all restaurants were closed by other company. How to make users order other food?

• Solution: 8 + 9 = 17

Pattern is a solution to a recurring problem in a context

• Context: A CEO of a company

• Problem: tough competition among the delivery services. How to get more orders?

• Solution: Binding card then ordering for free. Threaten to selling card information and shut down server.

Pattern is a proven solution to a recurring problem in a context

• Context: A CEO of a company

• Problem: tough competition among the delivery services. How to get more orders?

• Solution: Send coupons, hold activities. Buy UberEATs, FoodPanda…

Pattern is a proven solution to a recurring problem in a

specific context

• Context: tough competition among the delivery services. A CEO of a company with limited budget

• Problem: How to get more orders?

• Solution: Send coupons, hold activities …

Pattern is a proven solution to a recurring problem in a specific context

Each pattern describes a problem that occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.

— Christopher Alexander

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• Name • Context • Problem • Solution • Force • Resulting Context

ContextProblem

Elements of Pattern

Solution(Form)Force

Why learn Design Patterns?

• Common ground for communication • Not for excluding outsiders • • Reusable is so hard • Standing on the shoulders of giants - Issac Newton

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Erich Gamma, Richard Helm,

Ralph Johnson, John Vlissides

Gang of Four (GoF)1994 ~

References

by Teddy Chen

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• Purpose 1. Creational 2. Structural 3. Behavioral

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• Scope 1. Class: static 2. Object: dynamic

purpose

creational structural behavioral

scope

class Factory Method Adaptor Interpreter Template Method

object

Abstract Factory Builder

Prototype Singleton

Adapter Bridge

Composite Decorator Facade

Flyweight Proxy

Chain of Responsibility Command

Iterator Mediator Memento Observer

State Strategy Visitor

How to learn Design Patterns?

• Joshua Kerievsky : A Learning Guide to Design Patterns

• One more time

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message (request)

method (operation) encapsulation

signature (name, parameters, return type)

• Design: Abstraction

• Flow & Algorithms: Strategy

• State: State

• type: a specific interface

Dynamic BindingPolymorphism

Program to an interface, not an implementation

• Clients remain unaware of the specific types or class • Clients only know about the abstract class defining the interface.

Inheritance vs. Composition

• White box & Black Box • Compile time & Runtime

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Favor object composition over class inheritance

Delegate

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• Class composition

• Class inheritance

• Parameterized type (Generic, Template) Array<String>()

Reuse

aggregation

acquaintance(association, using)

has-A (part of)

using (know of)

Toolkit vs.

Framework

References

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• https://s-media-cache-ak0.pinimg.com/736x/8d/dc/a5/8ddca508d43902192028cc0f0f1ad763.jpg

• https://upload.wikimedia.org/wikipedia/en/b/bf/The_Timeless_Way_of_Building.jpg

• https://d2hsbzg80yxel6.cloudfront.net/images/85778/original/9572054112.jpg

• https://images-na.ssl-images-amazon.com/images/I/81r69ARQevL.jpg

• https://d2hsbzg80yxel6.cloudfront.net/images/49583/original/9789866761799.jpg

• https://images-na.ssl-images-amazon.com/images/I/41Uat%2B4bqAL._SX258_BO1,204,203,200_.jpg

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