一. for & 区间运算符

//闭区间 closedRange
for index in 0...3 {
    print(index)    //0 1 2 3
}
//开区间 Range
for index in 0..<3 {
    print(index)    //0 1 2
}
//单侧区间 partialRangeThrough  partial:美  [ˈpɑːrʃ(ə)l] adj. 部分的，不完全的；偏袒的，不公平的；偏爱的
let chars = ["a", "b", "c"]
for char in chars[0...] {
    print(char)     //a b c
}
for char in chars[...2] {
    print(char)     //a b c
}
for char in chars[...] {
    print(char)     //a b c
}
for char in chars {
    print(char)     //a b c
}
//range是否包含
let range = 0...5
range.contains(-1)  //false
range.contains(5)   //true

let rang1 = "aa"..."zz"
rang1.contains("b") //true
rang1.contains("bb")//true

//带间隔的区间
//stride 美  [straɪd] n. 大步，阔步；步态，步伐；步距，步幅；步速；进展
for tick in stride(from: 1, through: 10, by: 2) {
    print("tick_\(tick)")
}

二. switch

// 不需要加{}
// 不需要加break
// 想要贯穿,使用fallThrough
let switchNum = 1
switch switchNum {
case 1:
    print("1")
    fallthrough
case 2:
    print("2")
case 3,4,5:
    print("3 4 5")
case 1..<5:
    print("1..5")
default:
    print("")
    break
}

//使用where做筛选过滤
let for_where = [1, 2, 3, 4, 5]
var for_sum = 0
for num in for_where where num > 3 {
    for_sum += num
}
print("for_sum=\(for_sum)")

//可选项使用switch
var o: Int? = 10
switch o {
case let p?://如果不为nil,则解包并把值给p
    print(p)
case nil:
    print("nil")
}

//和上面一样的用途
switch o {
case .some(p):
    print(p)
case .none:
    print("nil")
}