Swift学习笔记。

空合运算符(Nil Coalescing Operator) a ?? b ---> a != nil ? a! : b a必须是optional的：

let defaultColorName = "red"
var userDefinedColorName: String?
var colorNameToUse = userDefinedColorName ?? defaultColorName

userDefinedColorName = "gree"
colorNameToUse = userDefinedColorName ?? defaultColorName

for index in 1...5 {
    print(index)
}

image = UIImage(named: "SetOperations")


let oddDigits: Set = [1,3,5,7,9]
let evenDigits: Set = [0,2,4,6,8]
let singleDigitPrimeNumbers: Set = [2,7]
// 并集
oddDigits.union(evenDigits).sort()
// 交集
oddDigits.intersect(evenDigits).sort()
// 补集 
oddDigits.subtract(evenDigits).sort()


oddDigits.exclusiveOr(singleDigitPrimeNumbers).sort()


// 集合关系和比较
//使用“是否等”运算符(==)来判断两个集合是否包含相同的值。
//使用isSubsetOf(_:)方法来判断一个集合中的值是否也被包含在另外一个集合中。
//使用isSupersetOf(_:)方法来判断一个集合中包含的值是另一个集合中所有的值。
//使用isStrictSubsetOf(_:)或者isStrictSupersetOf(_:)方法来判断一个集合是否是另外一个集合的子集合或者父集合,并且和特定集合不相等。
//使用isDisjointWith(_:)方法来判断两个结合是否不含有相同的值。


image = UIImage(named: "setEulerDiagram")


let houseAnimals: Set = ["1","2"]
let farmAnimals: Set = ["1","2","3","4","5"]
let cityAnimals: Set = ["6","7"]
houseAnimals.isSubsetOf(farmAnimals)
// true
farmAnimals.isSupersetOf(houseAnimals)
// true
farmAnimals.isDisjointWith(cityAnimals)
// true

Switch 与其他语言不同，不用在每个case中写break，swift只会执行一个case。switch语句必须是完备的。这就是说，每一个可能的值都必须至少有一个 case 分支与之对应。在某些不可能涵盖所有值的情况下，你可以使用默认（default）分支满足该要求，这个默认分支必须在switch语句的最后面。case中的条件可以是多个，并且可以是任意类型

let approximateCount = 62
let countedThings = "moons orbiting Saturn"
var naturalCount: String
switch approximateCount {
case 0:
    naturalCount = "no"
case 1..<5:
    naturalCount = "a few"
case 5..<12:
    naturalCount = "several"
case 12..<100:
    naturalCount = "dozens of"
case 100..<1000:
    naturalCount = "hundreds of"
default:
    naturalCount = "many"
}
print("There are (naturalCount) (countedThings).")

let somePoint = (1,1)
switch somePoint {
case (0,0):
    print("(0,0) is at the origin")
case (_,0): // x任意 y==0
    print("((somePoint.0),0) is on the x-axis")
case (0,_): // x==0 y任意
    print("(0,(somePoint.1)) is on the y-axis")
case (-2...2,-2...2):
    print("((somePoint.0),(somePoint.1)) is inside the box")
default:
    print("((somePoint.0),(somePoint.1)) is outside the box")
}
image = UIImage(named: "coordinateGraphSimple")
// 虽然上面如果point为(0,0)的时候，会满足所有的case，但是swift只会选择第一个满足的执行

let anotherPoint = (2,0)
// 注意下面是没有default的
// 下面的let声明，可以改成var声明
switch anotherPoint {
case (let x,0):
    print("on the x-axis with an x value of (x)")
case (0,let y):
    print("on the y-axis whth a y value of (y)")
case let (x,y):
    print("somewhere else at ((x),(y))")
}
image = UIImage(named: "coordinateGraphMedium")

// Where
let yetAnotherPoint = (1,-1)
switch yetAnotherPoint {
case let (x,y) where x == y:
    print("((x),(y)) is on the line x == y")
case let (x,y) where x == -y:
    print("((x),(y)) is on the line x == -y")
case let (x,y):
    print("((x),(y)) is just some arbitrary point")
}
image = UIImage(named: "coordinateGraphComplex")

let integerToDescribe = 5
var description = "The number (integerToDescribe) is"
switch integerToDescribe {
case 2,11,13,17,19:
    description += " a prime number,and also"
    fallthrough
default:
    description += " an integer."
}
print(description)

（编辑：李大同）

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