Swift编程指南：Raywenderlich教程

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"《swift by tutorials》是由raywenderlich.com网站提供的教程，专注于Swift语言的学习，适合苹果平台（iOS和Mac）的软件开发。" 本文档是《Swift by Tutorials》的一部分，由raywenderlich.com的教程团队编写，包括Colin Eberhardt和Matt Galloway等人。该教程涵盖了Swift编程语言的基础知识，旨在帮助开发者入门并掌握Swift。内容可能包括源代码示例，但明确指出未经版权所有者事先书面许可，不得复制或分发任何部分。在法律免责声明中，该书及其所有相关材料（如源代码）均按“原样”提供，不提供任何形式的明示或暗示保证，包括但不限于适销性、特定用途适用性和非侵权的保证。作者和版权持有者不对因软件或其使用或其他交易而产生的任何索赔、损害或其他责任负责，无论是在合同、侵权或其他情况下。目录显示，教程内容将从基础语言知识开始，分为两个部分讲解，随后将深入到类（Classes）等更高级的主题。这表明教程将逐步引导读者理解Swift的关键概念，从基本语法到面向对象编程的核心元素。在学习Swift时，你将可能接触到以下知识点： 1. **变量和常量（Variables and Constants）**：了解如何声明和使用let（常量）和var（变量）。 2. **数据类型（Data Types）**：包括整型（Int, UInt等）、浮点型（Double, Float）、布尔型（Bool）、字符串（String）以及元组（Tuple）。 3. **操作符（Operators）**：加减乘除、比较操作符以及位操作符等。 4. **控制流（Control Flow）**：条件语句（if-else）、循环（for-in, while, do-while）和switch语句。 5. **函数（Functions）**：定义和调用函数，参数和返回值，以及闭包（Closure）。 6. **数组和集合（Arrays and Sets）**：了解如何创建、遍历和操作数组和集合。 7. **字典（Dictionaries）**：键值对的存储和访问方法。 8. **类和结构体（Classes and Structures）**：面向对象编程的基础，包括初始化、属性、方法、继承、协议和扩展。 9. **枚举（Enums）**：用于定义一组相关的值，可以带有关联值和计算属性。 10. **可选值（Optionals）**：Swift的错误处理机制，防止空指针异常。 11. **类型别名（Type Aliases）**：为已存在的类型创建新的名字。 12. **泛型（Generics）**：使代码更具通用性，可以在多种类型上工作。 13. **协议（Protocols）**：定义一组要求遵循的规则，可以被类、结构体或枚举遵循。 14. **扩展（Extensions）**：向已有的类型添加新功能，无需修改原始实现。 15. **错误处理（Error Handling）**：通过do-catch结构处理运行时可能出现的错误。通过这个教程，开发者可以系统地学习Swift编程，逐步掌握构建iOS和Mac应用所需的技能。

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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