a swift tour

转载:官方文档

//: # A Swift Tour

//:

//: Tradition suggests that the first program in a new language should print the words “Hello, world!” on the screen. In Swift, this can be done in a single line:

//:

//传统惯例,打印hello world

print("Hello, world!")

下载链接:github

//: If you have written code in C or Objective-C, this syntax looks familiar to you—in Swift, this line of code is a complete program. You don’t need to import a separate library for functionality like input/output or string handling. Code written at global scope is used as the entry point for the program, so you don’t need a `main()` function. You also don’t need to write semicolons at the end of every statement.

//:

//: This tour gives you enough information to start writing code in Swift by showing you how to accomplish a variety of programming tasks. Don’t worry if you don’t understand something—everything introduced in this tour is explained in detail in the rest of this book.

//:

 Simple Values

//:

//: Use `let` to make a constant and `var` to make a variable. The value of a constant doesn’t need to be known at compile time, but you must assign it a value exactly once. This means you can use constants to name a value that you determine once but use in many places.

//:

//不用分号,在每行的末尾

//常量与变量

//常量用在多次使用的情况下,常量赋值一次

var myVariable = 42

myVariable = 50

let myConstant = 42

//类型检查,常量变量如果类型不匹配,会编译报错,基本数据类型之间不可以强转

//: A constant or variable must have the same type as the value you want to assign to it. However, you don’t always have to write the type explicitly. Providing a value when you create a constant or variable lets the compiler infer its type. In the example above, the compiler infers that `myVariable` is an integer because its initial value is an integer.

//:

//: If the initial value doesn’t provide enough information (or if there is no initial value), specify the type by writing it after the variable, separated by a colon.

//:

let implicitInteger = 70

let implicitDouble = 70.0

let explicitDouble: Double =70

//实验

let  Fl64:Float64=98.4

//: - Experiment:

//: Create a constant with an explicit type of `Float` and a value of `4`.

//:

//: Values are never implicitly converted to another type. If you need to convert a value to a different type, explicitly make an instance of the desired type.

//:

let label = "The width is "

let width = 94

let widthLabel = label +String(width)

//实验,当把String删除,编译报错 "加号操作符不可以操作int和string因为类型不一致,无法推断

//let widthLabel = label + width

//: - Experiment:

//: Try removing the conversion to `String` from the last line. What error do you get?

//:

//: There’s an even simpler way to include values in strings: Write the value in parentheses, and write a backslash (`\`) before the parentheses. For example:

//:

let apples = 3

let oranges = 5

//插值运算

let appleSummary ="I have\(apples) apples."

let fruitSummary ="I have\(apples +oranges) pieces of fruit."

//实验:

let floatNumbers=24.4

let name="李chance"

let greeting="\(name) have\(floatNumbers)"

//: - Experiment:

//: Use `\()` to include a floating-point calculation in a string and to include someone’s name in a greeting.

//:

//: Create arrays and dictionaries using brackets (`[]`), and access their elements by writing the index or key in brackets. A comma is allowed after the last element.

//:

//数组最后一行多加一个逗号不影响任何结果,但是字典多加逗号是不被允许的

var shoppingList = ["catfish","water","tulips","blue paint"]

shoppingList[1] ="bottle of water"

var occupations = [

    "Malcolm":"Captain",

    "Kaylee":"Mechanic"

 ]

occupations["Jayne"] ="Public Relations"

//: To create an empty array or dictionary, use the initializer syntax.

//:

//初始化方法,空数组,空字典

let emptyArray = [String]()

let emptyDictionary = [String:Float]()

//: If type information can be inferred, you can write an empty array as `[]` and an empty dictionary as `[:]`—for example, when you set a new value for a variable or pass an argument to a function.

//:

//将字典和数组置空

shoppingList = []

occupations = [:]

shoppingList

occupations

 Control Flow

//:

//: Use `if` and `switch` to make conditionals, and use `for`-`in`, `for`, `while`, and `repeat`-`while` to make loops. Parentheses around the condition or loop variable are optional. Braces around the body are required.

//:

let individualScores = [75,43,103,87,12]

var teamScore = 0

for score inindividualScores {

    if score >50 {

        teamScore +=3

    } else {

        teamScore +=1

    }

}

print(teamScore)

//条件表达式必须是一个Boolean表达式

//: In an `if` statement, the conditional must be a Boolean expression—this means that code such as `if score { ... }` is an error, not an implicit comparison to zero.

//:

//: You can use `if` and `let` together to work with values that might be missing. These values are represented as optionals. An optional value either contains a value or contains `nil` to indicate that a value is missing. Write a question mark (`?`) after the type of a value to mark the value as optional.

//:

var optionalString: String? ="Hello"

print(optionalString ==nil)

var optionalName: String? ="John Appleseed"

var greeting = "Hello!"

if let name =optionalName {

    greeting ="Hello,\(name)"

}

//实验

var optionalString1: String?

print(optionalString1 ==nil)

//if 和 let结合可以防止值丢失

var optionalName1: String?

var greeting1 = "Hello!"

if let name1 =optionalName1 {

    greeting1 ="Hello,\(name1)"

}

//: - Experiment:

//: Change `optionalName` to `nil`. What greeting do you get? Add an `else` clause that sets a different greeting if `optionalName` is `nil`.

//:

//: If the optional value is `nil`, the conditional is `false` and the code in braces is skipped. Otherwise, the optional value is unwrapped and assigned to the constant after `let`, which makes the unwrapped value available inside the block of code.

//:

//: Another way to handle optional values is to provide a default value using the `??` operator. If the optional value is missing, the default value is used instead.

//:

//常量可选值为nil

//运用??如果为nil组使用全名

let nickName: String? =nil

let fullName: String = "John Appleseed lee"

let informalGreeting = "Hi\(nickName ??fullName)"

//实验:

var nickName1: String? =nil

nickName1="chance"

let fullName1: String ="无心禅师"

let informalGreeting1 = "Hi \(nickName1 ??fullName1)"

//: Switches support any kind of data and a wide variety of comparison operations—they aren’t limited to integers and tests for equality.

//:

//switch支持任何类型的数据,和多样性的比较操作,不再局限为整型比较

let vegetable = "red pepper"

switch vegetable {

    case"celery":

        print("Add some raisins and make ants on a log.")

    case"cucumber","watercress":

        print("That would make a good tea sandwich.")

    case let x where x.hasSuffix("pepper"):

        print("Is it a spicy\(x)?")

    default:

        print("Everything tastes good in soup.")

}

//实验,不用加break,不用强制加break,执行完一个case自动回跳出

//另外     default绝对不能省掉,编译都会报错

let xingshi = "赵pepper"

switch xingshi {

case "孙":

    print("Add some raisins and make ants on a log.")

case "李","郑":

    print("That would make a good tea sandwich.")

case let xwhere x.hasSuffix("pepper"):

    print("Is it a spicy\(x)?")

default:

    print("not found.")

}

//: - Experiment:

//: Try removing the default case. What error do you get?

//:

//: Notice how `let` can be used in a pattern to assign the value that matched the pattern to a constant.

//:

//: After executing the code inside the switch case that matched, the program exits from the switch statement. Execution doesn’t continue to the next case, so there is no need to explicitly break out of the switch at the end of each case’s code.

//:

//: You use `for`-`in` to iterate over items in a dictionary by providing a pair of names to use for each key-value pair. Dictionaries are an unordered collection, so their keys and values are iterated over in an arbitrary order.

//:

let interestingNumbers = [

    "Prime": [2,3,5,7,11,13],

    "Fibonacci": [1,1,2,3,5,8],

    "Square": [1,4,9,16,25],

]

var largest = 0

var kindString:String?

for (kind, numbers) ininterestingNumbers {

    

    for numberin numbers {

        if number >largest {

            largest = number

            kindString=kind

        }

    }

}

print(largest)

//实验找到所属分类

print(kindString)

//: - Experiment:

//: Add another variable to keep track of which kind of number was the largest, as well as what that largest number was.

//:

//: Use `while` to repeat a block of code until a condition changes. The condition of a loop can be at the end instead, ensuring that the loop is run at least once.

//:

var n = 2

while n <100 {

    n = n * 2

}

print(n)

//c与oc的do-while改为 repeat-while

var m = 2

repeat {

    m = m * 2

} while m < 100

print(m)

//: You can keep an index in a loop by using `..<` to make a range of indexes.

//:

//半开区间

var total = 0

for i in0..<4 {

    total += i

}

print(total)

//实验,闭区间

total=0

for i in0...4 {

    total += i

}

print(total)

//: Use `..<` to make a range that omits its upper value, and use `...` to make a range that includes both values.

//:

 Functions and Closures

//:

//: Use `func` to declare a function. Call a function by following its name with a list of arguments in parentheses. Use `->` to separate the parameter names and types from the function’s return type.

//:

func greet(name: String, day:String, lunch:String) ->String {

    return"Hello\(name), today is\(day),lunch is\(lunch)."

}

greet("Bob", day:"Tuesday" ,lunch:"noodle")

//第一个参数的形参可以省略的

//: - Experiment:

//: Remove the `day` parameter. Add a parameter to include today’s lunch special in the greeting.

//:

//: Use a tuple to make a compound value—for example, to return multiple values from a function. The elements of a tuple can be referred to either by name or by number.

//:

//返回值可以是元组类型

func calculateStatistics(scores: [Int]) -> (min:Int, max:Int, sum:Int) {

    var min = scores[0]

    var max = scores[0]

    var sum =0

    for scorein scores {

        if score > max {

            max = score

        } elseif score < min {

            min = score

        }

        sum += score

    }

    return (min, max, sum)

}

let statistics = calculateStatistics([5,3,100,3,9])

print(statistics.sum)

//返回值的元组可以用函数名加下标的方式调用或者参数名字调用

print(statistics.2)

print(statistics.1)

print(statistics.max)

print(statistics.0)

print(statistics.min)

//: Functions can also take a variable number of arguments, collecting them into an array.

//:

//可以将一系列的参数装进一个数组里

func sumOf(numbers: Int...) ->Int {

    var sum =0

    for numberin numbers {

        sum += number

    }

    return sum

}

sumOf()

sumOf(42,597,12)

//实验,求平均值

func averge(numbers:Int...)->Double {

    var aver:Double=0.0

    var sum =0

    

    for numberin numbers {

        sum+=number;

    }

    aver = (Double)(sum/numbers.count)

    return aver;

}

averge(42,597,112)

//: - Experiment:

//: Write a function that calculates the average of its arguments.

//:

//: Functions can be nested. Nested functions have access to variables that were declared in the outer function. You can use nested functions to organize the code in a function that is long or complex.

//:

func returnFifteen() -> Int {

    var y =10

    func add() {

        y += 5

    }

    add()

    return y

}

returnFifteen()

//: Functions are a first-class type. This means that a function can return another function as its value.

//:

//函数是一等类型,可以以其他函数作为返回值

func makeIncrementer() -> ((Int) ->Int) {

    func addOne(number:Int) ->Int {

        return1 + number

    }

    returnaddOne

}

var increment = makeIncrementer()

increment(7)

//: A function can take another function as one of its arguments.

//:

//函数是一等类型,可以以其他函数作为参数

func hasAnyMatches(list: [Int], condition: (Int) ->Bool) -> Bool {

    for itemin list {

        if condition(item) {

            returntrue

        }

    }

    returnfalse

}

func lessThanTen(number: Int) -> Bool {

    return number <10

}

var numbers = [20,19,7,12]

hasAnyMatches(numbers, condition:lessThanTen)

//: Functions are actually a special case of closures: blocks of code that can be called later. The code in a closure has access to things like variables and functions that were available in the scope where the closure was created, even if the closure is in a different scope when it is executed—you saw an example of this already with nested functions. You can write a closure without a name by surrounding code with braces (`{}`). Use `in` to separate the arguments and return type from the body.

//:

//函数是一种特殊的闭包

numbers.map({

    (number: Int) ->Intin

    let result =3 * number

    return result

})

//实验

//重写一个闭包来对所有奇数返回0。

var numberArray = [2,3,7,12]

print (numberArray.map({

    (number: Int) ->Intin

    var result = number

    if (!((number%2)==0))

    {

        result=0

    }

    print(result)

    return result;

})

)

numberArray

//: - Experiment:

//: Rewrite the closure to return zero for all odd numbers.

//:

//: You have several options for writing closures more concisely. When a closure’s type is already known, such as the callback for a delegate, you can omit the type of its parameters, its return type, or both. Single statement closures implicitly return the value of their only statement.

//:

let mappedNumbers = numbers.map({ numberin3 * number })

print(mappedNumbers)

//: You can refer to parameters by number instead of by name—this approach is especially useful in very short closures. A closure passed as the last argument to a function can appear immediately after the parentheses. When a closure is the only argument to a function, you can omit the parentheses entirely.

//:

//降序

let sortedNumbers = numbers.sort { $0 > $1 }

print(sortedNumbers)

 Objects and Classes

//:

//: Use `class` followed by the class’s name to create a class. A property declaration in a class is written the same way as a constant or variable declaration, except that it is in the context of a class. Likewise, method and function declarations are written the same way.

//:

class Shape {

    var numberOfSides =0

    func simpleDescription() ->String {

        return"A shape with\(numberOfSides) sides."

    }

    //实验

    let name="正方形"

    func whichSide(index:Int) ->String {

        return"正方形的第\(index)条边"

    }

}

//: - Experiment:

//: Add a constant property with `let`, and add another method that takes an argument.

//:

//: Create an instance of a class by putting parentheses after the class name. Use dot syntax to access the properties and methods of the instance.

//:

var shape = Shape()

shape.numberOfSides =7

var shapeDescription = shape.simpleDescription()

shape.name;

shape.whichSide(3)

//: This version of the `Shape` class is missing something important: an initializer to set up the class when an instance is created. Use `init` to create one.

//:

class NamedShape {

    var numberOfSides:Int =0

    var name:String

    

    init(name:String) {

        self.name = name

    }

 //实验

//初始化构造器,必须传的参数

    init(name:String,sides:Int) {

       self.name = name

        self.numberOfSides=sides

    }

    func simpleDescription() ->String {

       return"A shape with\(numberOfSides) sides."

    }

}

var nameSh = NamedShape(name:"三角形",sides:3)

 nameSh.simpleDescription();

//: Notice how `self` is used to distinguish the `name` property from the `name` argument to the initializer. The arguments to the initializer are passed like a function call when you create an instance of the class. Every property needs a value assigned—either in its declaration (as with `numberOfSides`) or in the initializer (as with `name`).

//:

//: Use `deinit` to create a deinitializer if you need to perform some cleanup before the object is deallocated.

//:

//: Subclasses include their superclass name after their class name, separated by a colon. There is no requirement for classes to subclass any standard root class, so you can include or omit a superclass as needed.

//:

//: Methods on a subclass that override the superclass’s implementation are marked with `override`—overriding a method by accident, without `override`, is detected by the compiler as an error. The compiler also detects methods with `override` that don’t actually override any method in the superclass.

//:

//super父类

class Square: NamedShape {

    var sideLength:Double

    init(sideLength:Double, name:String) {

        self.sideLength = sideLength

        //调用父类的初始化方法

        super.init(name: name)

        numberOfSides =4

    }

    func area() -> Double {

        returnsideLength *sideLength

    }

    //重载父类方法

    overridefunc simpleDescription() ->String {

        return"A square with sides of length\(sideLength)."

    }

}

let test = Square(sideLength:5.2, name:"my test square")

test.area()

test.simpleDescription()

//实验

class Circle: NamedShape {

    var radious:Double

    let PI=3.1415926

    

    init(radious:Double, name:String) {

        self.radious = radious

        //调用父类的初始化方法

        super.init(name: name)

    }

    

    func area() -> Double {

        returnPI *radious*radious

    }

    

    //重载父类方法

    overridefunc simpleDescription() ->String {

        return"A circle with radious of radious\(radious)."

    }

}

let testC = Circle(radious:5.2, name:"my test Circe")

testC.area()

testC.simpleDescription()

//: - Experiment:

//: Make another subclass of `NamedShape` called `Circle` that takes a radius and a name as arguments to its initializer. Implement an `area()` and a `simpleDescription()` method on the `Circle` class.

//:

//: In addition to simple properties that are stored, properties can have a getter and a setter.

//:

class EquilateralTriangle: NamedShape {

    var sideLength:Double =0.0

    init(sideLength:Double, name:String) {

        self.sideLength = sideLength

        super.init(name: name)

        numberOfSides =3

    }

    var perimeter:Double {

        get {

             return4.0 *sideLength

        }

        set {

            sideLength = newValue /3.0

        }

    }

    overridefunc simpleDescription() ->String {

        return"An equilateral triangle with sides of length\(sideLength)."

    }

}

var triangle = EquilateralTriangle(sideLength:4.2, name:"a triangle")

print(triangle.perimeter)

triangle.perimeter =100

print(triangle.sideLength)

//注意newValue

//: In the setter for `perimeter`, the new value has the implicit name `newValue`. You can provide an explicit name in parentheses after `set`.

//:

//: Notice that the initializer for the `EquilateralTriangle` class has three different steps:

//:

//: 1. Setting the value of properties that the subclass declares.

//:

//: 1. Calling the superclass’s initializer.

//:

//: 1. Changing the value of properties defined by the superclass. Any additional setup work that uses methods, getters, or setters can also be done at this point.

//:

//: If you don’t need to compute the property but still need to provide code that is run before and after setting a new value, use `willSet` and `didSet`. The code you provide is run any time the value changes outside of an initializer. For example, the class below ensures that the side length of its triangle is always the same as the side length of its square.

//:

//用willSet和didSet这两个特性来监视属性的除初始化之外的属性值变化

class TriangleAndSquare {

    var triangle:EquilateralTriangle {

        willSet {

            square.sideLength = newValue.sideLength

        }

    }

    var square:Square {

        willSet {

            triangle.sideLength = newValue.sideLength

        }

    }

    init(size:Double, name:String) {

        square =Square(sideLength: size, name: name)

        triangle =EquilateralTriangle(sideLength: size, name: name)

    }

}

var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")

print(triangleAndSquare.square.sideLength)

print(triangleAndSquare.triangle.sideLength)

triangleAndSquare.square =Square(sideLength:50, name: "larger square")

print(triangleAndSquare.triangle.sideLength)

//测试

class Person {

    

    // 年龄属性

    var age:Int?

    

    // 姓名属性

    var name:String? {

        

        willSet{

            print("willSet")

        }

        

        didSet{

            print("didSet")

        }

    }

}

var  p=Person()

p.name="李美双"

//: When working with optional values, you can write `?` before operations like methods, properties, and subscripting. If the value before the `?` is `nil`, everything after the `?` is ignored and the value of the whole expression is `nil`. Otherwise, the optional value is unwrapped, and everything after the `?` acts on the unwrapped value. In both cases, the value of the whole expression is an optional value.

//:

//可选值链,只要有一个可选为nil则不往下传递

let optionalSquare: Square? =Square(sideLength:2.5, name: "optional square")

let sideLength = optionalSquare?.sideLength

 Enumerations and Structures

//:

//: Use `enum` to create an enumeration. Like classes and all other named types, enumerations can have methods associated with them.

//:

enum Rank: Int {

    //枚举可以是整型

    //可以多个case

    //rawValue

    case Ace =1

    case Two, Three, Four, Five, Six, Seven, Eight, Nine, Ten

    case Jack, Queen, King

    func simpleDescription() ->String {

        switchself {

            case .Ace:

                return"ace"

            case .Jack:

                return"jack"

            case .Queen:

                return"queen"

            case .King:

                return"king"

            default:

                returnString(self.rawValue)

        }

    }

    

}

let ace = Rank.Ace

let aceRawValue = ace.rawValue

let ace1=Rank.Jack;

ace1.simpleDescription();

let ace2=Rank.Three;

ace2.simpleDescription();

//: - Experiment:

//: Write a function that compares two `Rank` values by comparing their raw values.

//:

//: By default, Swift assigns the raw values starting at zero and incrementing by one each time, but you can change this behavior by explicitly specifying values. In the example above, `Ace` is explicitly given a raw value of `1`, and the rest of the raw values are assigned in order. You can also use strings or floating-point numbers as the raw type of an enumeration. Use the `rawValue` property to access the raw value of an enumeration case.

//:

//: Use the `init?(rawValue:)` initializer to make an instance of an enumeration from a raw value.

//:

if let convertedRank =Rank(rawValue:3) {

    let threeDescription = convertedRank.simpleDescription()

}

//: The case values of an enumeration are actual values, not just another way of writing their raw values. In fact, in cases where there isn’t a meaningful raw value, you don’t have to provide one.

//:

enum Suit {

    case Spades, Hearts, Diamonds, Clubs

    func simpleDescription() ->String {

        switchself {

            case .Spades:

                return"spades"

            case .Hearts:

                return"hearts"

            case .Diamonds:

                return"diamonds"

            case .Clubs:

                return"clubs"

        }

    }

    //实验

    func color() ->String {

        switchself {

        case .Spades,.Hearts:

            return"black"

        default:

            return"red"

        }

    }

}

let hearts = Suit.Hearts

let heartsDescription = hearts.simpleDescription()

let colorSuit=hearts.color()

//: - Experiment:

//: Add a `color()` method to `Suit` that returns “black” for spades and clubs, and returns “red” for hearts and diamonds.

//:

//: Notice the two ways that the `Hearts` case of the enumeration is referred to above: When assigning a value to the `hearts` constant, the enumeration case `Suit.Hearts` is referred to by its full name because the constant doesn’t have an explicit type specified. Inside the switch, the enumeration case is referred to by the abbreviated form `.Hearts` because the value of `self` is already known to be a suit. You can use the abbreviated form anytime the value’s type is already known.

//:

//: Use `struct` to create a structure. Structures support many of the same behaviors as classes, including methods and initializers. One of the most important differences between structures and classes is that structures are always copied when they are passed around in your code, but classes are passed by reference.

//:

//利用结构体将两个枚举作为参数

struct Card {

    var rank:Rank

    var suit:Suit

    func simpleDescription() ->String {

        return"The\(rank.simpleDescription()) of \(suit.simpleDescription())"

    }

}

let threeOfSpades = Card(rank: .Three, suit: .Spades)

let threeOfSpadesDescription = threeOfSpades.simpleDescription()

//: - Experiment:

//: Add a method to `Card` that creates a full deck of cards, with one card of each combination of rank and suit.

//:

//: An instance of an enumeration case can have values associated with the instance. Instances of the same enumeration case can have different values associated with them. You provide the associated values when you create the instance. Associated values and raw values are different: The raw value of an enumeration case is the same for all of its instances, and you provide the raw value when you define the enumeration.

//:

//: For example, consider the case of requesting the sunrise and sunset time from a server. The server either responds with the information or it responds with some error information.

//:

//枚举两个方法

enum ServerResponse {

    case Result(String,String)

    case Failure(String)

    case Timeout(String)

}

let success = ServerResponse.Result("6:00 am","8:09 pm")

let failure = ServerResponse.Failure("Out of cheese.")

let timeout = ServerResponse.Timeout("60秒超时")

switch success {

    case let .Result(sunrise, sunset):

        print("Sunrise is at\(sunrise) and sunset is at\(sunset).")

    case let .Failure(message):

        print("Failure... \(message)")

    case let .Timeout(time):

    print("超时连接")

}

//: - Experiment:

//: Add a third case to `ServerResponse` and to the switch.

//:

//: Notice how the sunrise and sunset times are extracted from the `ServerResponse` value as part of matching the value against the switch cases.

//:

 Protocols and Extensions

//:

//: Use `protocol` to declare a protocol.

//:

protocol ExampleProtocol {

     var simpleDescription:String {get }

    

    //可修改的

     mutatingfunc adjust()

}

//类,枚举,结构体都采用协议

//: Classes, enumerations, and structs can all adopt protocols.

//:

class SimpleClass: ExampleProtocol {

     var simpleDescription:String ="A very simple class."

     var anotherProperty:Int =69105

     func adjust() {

          simpleDescription +="  Now 100% adjusted."

     }

}

var a = SimpleClass()

a.adjust()

let aDescription =a.simpleDescription

struct SimpleStructure: ExampleProtocol {

     var simpleDescription:String ="A simple structure"

     mutatingfunc adjust() {

          simpleDescription +=" (adjusted)"

     }

}

var b = SimpleStructure()

b.adjust()

let bDescription =b.simpleDescription

//实验

enum EnumConformToProtocol: ExampleProtocol {

    case First(String), Second(String), Third(String)

    

    var simpleDescription:String {

        get {

            switchself {

            caselet .First(text):

                return text

            caselet .Second(text):

                return text

            caselet .Third(text):

                return text

            }

        }

    }

    mutatingfunc adjust() {

        switchself {

        caselet .First(text):

            self = .First(text +" (first case adjusted)")

        caselet .Second(text):

            self = .Second(text +" (second case adjusted)")

        caselet .Third(text):

            self = .Third(text +" (third case adjusted)")

        }

    }

}

var enumConformToProtocolTest =EnumConformToProtocol.First("FirstVal")

enumConformToProtocolTest.simpleDescription

enumConformToProtocolTest.adjust()

enumConformToProtocolTest.simpleDescription

enumConformToProtocolTest = EnumConformToProtocol.Third("ThirdVal")

enumConformToProtocolTest.simpleDescription

enumConformToProtocolTest.adjust()

enumConformToProtocolTest.simpleDescription

var e = EnumConformToProtocol.Second("Hello")

var text = e.simpleDescription

e.simpleDescription

text = e.simpleDescription

e.adjust()

text = e.simpleDescription

//: - Experiment:

//: Write an enumeration that conforms to this protocol.

//:

//: Notice the use of the `mutating` keyword in the declaration of `SimpleStructure` to mark a method that modifies the structure. The declaration of `SimpleClass` doesn’t need any of its methods marked as mutating because methods on a class can always modify the class.

//:

//: Use `extension` to add functionality to an existing type, such as new methods and computed properties. You can use an extension to add protocol conformance to a type that is declared elsewhere, or even to a type that you imported from a library or framework.

//:

extension Int:ExampleProtocol {

    var simpleDescription:String {

        return"The number\(self)"

    }

    mutatingfunc adjust() {

        self +=42

    }

 }

print(7.simpleDescription)

//实验,给double类型拓展一个求绝对值的属性

extension Double {

    var absoluteValue:Double {

        ifself >0.0 {

            returnself

        }

        else {

            return -1 *self

        }

    }

}

var minusTwo = -2.0

minusTwo.absoluteValue // 2.0

let minusThree = -3.0

minusThree.absoluteValue   // 3.0

(-4.0).absoluteValue // -4.0

//: - Experiment:

//: Write an extension for the `Double` type that adds an `absoluteValue` property.

//:

//: You can use a protocol name just like any other named type—for example, to create a collection of objects that have different types but that all conform to a single protocol. When you work with values whose type is a protocol type, methods outside the protocol definition are not available.

//:

let protocolValue: ExampleProtocol =a

print(protocolValue.simpleDescription)

// print(protocolValue.anotherProperty)  // Uncomment to see the error

//: Even though the variable `protocolValue` has a runtime type of `SimpleClass`, the compiler treats it as the given type of `ExampleProtocol`. This means that you can’t accidentally access methods or properties that the class implements in addition to its protocol conformance.

//:

Error Handling

//:

//: You represent errors using any type that adopts the `ErrorType` protocol.

//:

enum PrinterError: ErrorType {

    case OutOfPaper

    case NoToner

    case OnFire

}

//: Use `throw` to throw an error and `throws` to mark a function that can throw an error. If you throw an error in a function, the function returns immediately and the code that called the function handles the error.

//:

func sendToPrinter(printerName:String)throws ->String {

    if printerName =="Never Has Toner" {

        throwPrinterError.NoToner

    }

    return"Job sent"

}

//: There are several ways to handle errors. One way is to use `do`-`catch`. Inside the `do` block, you mark code that can throw an error by writing `try` in front of it. Inside the `catch` block, the error is automatically given the name `error` unless you can give it a different name.

//:

do {

    let printerResponse =trysendToPrinter("Bi Sheng")

    print(printerResponse)

} catch {

    print(error)

}

//: - Experiment:

//: Change the printer name to `"Never Has Toner"`, so that the `sendToPrinter(_:)` function throws an error.

//:

//: You can provide multiple `catch` blocks that handle specific errors. You write a pattern after `catch` just as you do after `case` in a switch.

//:

do {

    let printerResponse =trysendToPrinter("Gutenberg")

    print(printerResponse)

} catch PrinterError.OnFire {

    print("I'll just put this over here, with the rest of the fire.")

} catch let printerError asPrinterError {

    print("Printer error:\(printerError).")

} catch {

    print(error)

}

//: - Experiment:

//: Add code to throw an error inside the `do` block. What kind of error do you need to throw so that the error is handled by the first `catch` block? What about the second and third blocks?

//:

//: Another way to handle errors is to use `try?` to convert the result to an optional. If the function throws an error, the specific error is discarded and the result is `nil`. Otherwise, the result is an optional containing the value that the function returned.

//:

let printerSuccess = try?sendToPrinter("Mergenthaler")

let printerFailure = try?sendToPrinter("Never Has Toner")

//: Use `defer` to write a block of code that is executed after all other code in the function, just before the function returns. The code is executed regardless of whether the function throws an error. You can use `defer` to write setup and cleanup code next to each other, even though they need to be executed at different times.

//:

var fridgeIsOpen = false

let fridgeContent = ["milk","eggs","leftovers"]

func fridgeContains(itemName: String) -> Bool {

    fridgeIsOpen =true

    defer {

        fridgeIsOpen =false

    }

    let result =fridgeContent.contains(itemName)

    return result

}

fridgeContains("banana")

print(fridgeIsOpen)

Generics

//:

//: Write a name inside angle brackets to make a generic function or type.

//:

func repeatItem<Item>(item: Item, numberOfTimes: Int) -> [Item] {

    var result = [Item]()

    for _ in0..<numberOfTimes {

         result.append(item)

    }

    return result

}

repeatItem("dog", numberOfTimes:4)

//: You can make generic forms of functions and methods, as well as classes, enumerations, and structures.

//:

// Reimplement the Swift standard library's optional type

enum OptionalValue<Wrapped> {

    case None

    case Some(Wrapped)

}

var possibleInteger: OptionalValue<Int> = .None

possibleInteger = .Some(100)

//: Use `where` after the type name to specify a list of requirements—for example, to require the type to implement a protocol, to require two types to be the same, or to require a class to have a particular superclass.

//:

func anyCommonElements <T: SequenceType, U: SequenceTypewhereT.Generator.Element:Equatable,T.Generator.Element ==U.Generator.Element> (lhs:T,_ rhs:U) ->Bool {

    for lhsItemin lhs {

        for rhsItemin rhs {

            if lhsItem== rhsItem {

                returntrue

            }

        }

    }

   returnfalse

}

anyCommonElements([1,2,3], [3])

//实验

func isEquals<T: Comparable>(a:T, b:T) ->Bool {

    return (a== b)

}

isEquals("李美双", b:"lms")

//: - Experiment:

//: Modify the `anyCommonElements(_:_:)` function to make a function that returns an array of the elements that any two sequences have in common.

//:

//: Writing `<T: Equatable>` is the same as writing `<T where T: Equatable>`.

//: