Swift编程教程_v1.4：Swift语言基础

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"Swift_by_Tutorials_v1.4 - 更新至Swift 1.2，由raywenderlich.com教程团队创作的一本Swift编程教程" 在《Swift_by_Tutorials_v1.4》这本书中，读者将深入学习Swift编程语言的基础知识。这本书由raywenderlich.com的教程团队编写，包括Colin Eberhardt和Matt Galloway等人，覆盖了Swift 1.2版本的更新内容。此书旨在帮助开发者和学习者掌握Apple的这款强大且现代的编程语言。书中的章节分布广泛，从语言基础到更高级的概念，提供了逐步的学习路径。以下是书籍的部分内容概览： 1. **引言**：在这一部分，作者可能会介绍Swift语言的历史、设计哲学以及它如何对比Objective-C提供更简洁、安全的编程体验。可能还会讨论Swift在iOS、macOS和其他Apple平台开发中的重要性。 2. **第1章：语言基础I**：这一章涵盖了Swift的基础语法，包括变量和常量的声明（let和var），类型推断，数据类型（如Int, Double, String等），以及基本的运算符。此外，还可能涉及控制流语句（if-else, switch）和函数的定义与使用。 3. **第2章：语言基础II**：在这个阶段，读者会学习到更进阶的语言特性，比如枚举（enum）、结构体（struct）、类（class）以及它们之间的继承。同时，可能还会涉及协议（protocol）和扩展（extension）的概念，这是Swift中实现多态和代码复用的关键。 4. **第3章：类与对象**：本章可能深入探讨Swift的面向对象编程特性，包括初始化器（initializer）、析构函数（deinitializer）、属性（properties）、方法（methods）以及访问控制（access control）。同时，也可能介绍类型转换（type casting）和引用计数（reference counting）。 5. **其他章节**：书中后续章节可能涵盖闭包（closures）、数组和字典（arrays and dictionaries）、错误处理（error handling）、泛型（generics）、可选链（optional chaining）、Swift中的模块（modules）以及单元测试（unit testing）等内容。这本书不仅适合初学者，也对有一定经验的开发者有所帮助，因为它深入浅出地讲解了Swift语言的关键特性和最佳实践。请注意，由于版权原因，本书的具体内容、源代码和图像未经版权所有者书面许可不得复制或分发。书中的所有商标和注册商标均属于各自所有者。通过这本书，读者不仅可以提升Swift编程技能，还能了解到如何利用这些知识来构建高质量、健壮的应用程序。在学习过程中，读者可以跟随教程一步步实践，以确保理论与实践相结合，从而更好地理解和应用Swift语言。

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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