Swift编程实战教程：手把手教你学

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"Swift by Tutorials: A Hands-On Approach pdf" 是一本由 raywenderlich.com 教程团队编写的关于Swift编程语言的实战教程，由Colin Eberhardt和Matt Galloway等人共同撰写。这本书版权属于Razeware LLC，并且强调未经版权所有者事先书面许可，不得复制或分发任何部分。 Swift是苹果公司推出的一种编程语言，用于开发iOS、macOS、watchOS和tvOS的应用程序。本教程分为多个章节，深入浅出地介绍Swift的各个方面。在第一章“Language Basics I”中，读者将学习到Swift的基础语法，包括变量和常量的声明（let和var），数据类型（如Int、Double、String等），以及基本的控制流结构（if语句、for-in循环和while循环）。此外，还会涉及Swift中的打印命令（print）和注释的使用。第二章“Language Basics II”则更进一步，涵盖了函数（functions）和闭包（closures）的概念，这是Swift中重要的代码复用机制。同时，这一章还会讲解Swift的枚举（enums）和结构体（structs），这两种数据结构在面向对象编程中起到关键作用。函数参数、可变参数和默认参数值也是本章的重点。第三章“Classes”则深入探讨了面向对象编程的核心——类（classes）。读者会了解到如何定义类，包括属性（properties）、方法（methods）、初始化器（initializers）和继承（inheritance）。类的封装、多态和抽象概念也将在此章中得到阐述。书中的每个章节都配有实例，旨在帮助读者通过实践来掌握理论知识。读者还将接触到Swift的其他高级特性，如协议（protocols）、泛型（generics）、可选链（optional chaining）以及错误处理（error handling）等。同时，书中还会讨论Swift的.playground文件，这是一种便捷的测试和学习环境。 “Swift by Tutorials”是一本全面而实用的Swift学习资源，适合初学者和有一定经验的开发者，它将带领读者逐步探索Swift的每一个角落，从而精通这个强大的编程语言。通过这本教程，读者不仅能够学会如何编写Swift代码，还能理解其背后的逻辑和设计理念，从而更好地适应iOS和macOS的开发工作。

Swift by Tutorials Chapter 1: Language Basics I

raywenderlich.com Page 16

Open Xcode, select File\New Playground…, select the iOS platform and save the

file wherever you like:

A playground is a single Swift file that the template populates as follows:

As you enter your Swift code on the left-hand side of the view, the right-hand side

automatically displays the value of assignments and other useful hints about the

resulting application state. You don’t have to explicitly invoke a Build command

after making a change. In a playground, Xcode continually builds and executes your

code as you type.

Wouldn’t a playground be an excellent place to practice your Swift skills?

Swift by Tutorials Chapter 1: Language Basics I

raywenderlich.com Page 19

println(greeting)

This causes the compiler to report an error, type 'String' does not conform to

protocol 'IntegerLiteralConvertible', at the second line.

Type inference doesn’t weaken your application in any way; it simply saves

keystrokes by removing the need to specify types that are obvious to the compiler

(and hopefully to you). The simple example above shows type inference when

assigning literal values, but it will work everywhere within the language—for

example, when you create a variable and assign it a value from a function.

PRO TIP: We encourage you to use type inference extensively, as it results in

more concise and thus more readable code. However, if there is any instance

where you think adding an explicit type to a variable declaration would

enhance readability, there is certainly nothing wrong with doing so!

Let’s do some simple string manipulation. Update the code as follows:

var greeting = "Hello"

greeting = greeting + " World"

println(greeting)

The console output is now “Hello World” (surely you didn’t need a compiler to tell

you that!).

Swift strings are mutable—that is, you can change their values—where the

mutations have a much simpler syntax than their NSMutableString counterparts.

For example, you could change the above to use the more compact += compound

assignment operator.

There are many times you want to create a value that does not change. Creating

these values as variables is inherently unsafe since accidental assignments can and

do happen.

Swift makes it easy to change a variable into a constant. Update the first line of

code as follows:

let greeting = "Hello"

This results in an error at the second line of code: cannot assign to 'let' value

'greeting'.

You can control the mutability of the built-in Swift types (e.g., String, Int,

Dictionary) by using either the let or var keywords at the point of declaration.

This is in stark contrast to Objective-C and many other languages, where some

type implementations are inherently mutable, such as NSMutableArray, and some

are not, such as NSArray.

Swift by Tutorials Chapter 1: Language Basics I

raywenderlich.com Page 20

PRO-TIP: You should define values as constants wherever possible. This not

only makes your code more robust, it also allows the compiler to further

optimize your code, improving execution times. Thus, you will probably find

yourself using let far more often than var.

The use of let in order to make an instance of a type immutable isn’t restricted to

the built-in Swift types. Any structures (structs) that you define yourself also have

this behavior; however there are some subtle differences between constant

structures and classes. You can read more on this in Chapter 3, “Classes and

Structs”.

Change greeting back to a variable by changing the let to var, then add the

following line just before the println statement:

greeting.append(Character("!"))

This appends an exclamation mark to the end of the string, with the console

outputting the result, “Hello World!”.

The Swift String type has API methods like the above that allow you to manipulate

their values. However, these are quite limited in number. Fortunately, the Swift

String type is bridged to the Objective-C NSString type, providing all the API

methods with which you are no doubt familiar if you’ve used Objective-C.

To introduce these methods, update your playground as follows:

import Foundation

var greeting = "hello world".capitalizedString

println(greeting)

This results in the output “Hello World”.

With the first statement, you import the Foundation framework, which includes

NSString. This adds capitalizedString to Swift’s String.

Why not experiment with some of the other NSString API methods within the

playground? You can even append strings using stringByAppendingString if you

aren’t keen on the more compact Swift style!

import Foundation

var greeting = "hello".stringByAppendingString(" world")

println(greeting)

Finally, the Swift String is a value type. As a result, when you assign a string to a

variable, a constant, or pass it as an argument to a function, its value is copied.

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