Swift笔记 - 02.switch、case、where、标签语句、函数、可变参数、别名
Swift笔记 - 02.switch、case、where、标签语句、函数、可变参数、别名
switch/case复合条件匹配
switch也支持Character、String类型
let string = "Jack"
switch string {
case "Jack":
fallthrough
case "Rose":
print("Right person")
default:
break
} // Right person
switch string {
case "Jack", "Rose":
print("Right person")
default:
break
} // Right person
let character: Character = "a"
switch character {
case "a", "A":
print ("The letter A")
default:
print ("Not the letter A")
} // The letter A
switch/case的区间匹配与元组匹配
//区间匹配
let count = 62
switch count {
case 0:
print("none")
case 1..<5:
print("a few")
case 5..<12:
print("several")
case 12..<100:
print("dozens of")
case 100..<1000:
print("hundreds of")
default:
print("many")
} // dozens of
//元组匹配
let point = (1, 1)
switch point {
case (0, 0):
print("the origin")
case (_, 0):
print("on the x-axis")
case (0, _):
print("on the y-axis")
case (-2...2, -2...2):
print("inside the box")
default:
print("outside of the box")
} // inside the box
switch/case的值绑定
let point = (2, 0)
switch point {
case (let x, 0):
print("on the x-axis with an x value of \(x)")
case (0, let y):
print ("on the y-axis with a y value of \(y)")
case let (x, y) :
print ("somewhere else at (\(x), \(y))")
} // on the x-axis with an x value of 2
where 子句
let point = (1, -1)
switch point {
case let (x, y) where x == y:
print("on the line x == y")
case let (x, y) where x == -y:
print("on the line x == -y")
case let (x, y):
print("(\(x),\(y))isjustsomearbitrarypoint")
} // on the line x = -y
//将所有正数加起来
var numbers = [10, 20, -10, -20, 30, -30]
var sum = 0
for num in numbers where num > 0 {//使用where来过滤num
sum += num
}
print(sum) // 60
标签语句
outer: for i in 1...4 {
for k in 1...4 {
if k == 3 {
continue outer
}
if i == 3 {
break outer
}
print("i == \(i), k == \(k)")
}
}
函数的隐式返回
如果整个函数体是一个单一表达式，那么函数会隐式返回这个表达式
func sum(v1: Int, v2: Int) -> Int {
v1 + v2
}
sum(v1: 10, v2: 20) // 30
Swift可变参数
func sum(_ numbers: Int...) -> Int {
var total = 0
for number in numbers {
total += number
}
return total
}
sum(10, 20, 30, 40) // 100
- 一个函数最多只能有1个可变参数
- 紧跟在可变参数后面的参数不能省略参数标签
//参数string不能省略标签
func test(_ numbers: Int..., string: String, _ other: String) { }
test(10, 20, 30, string: "Jack", "Rose")
函数类型作为函数返回值
func next (_ input: Int) -> Int {
input + 1
}
func previous(_ input: Int) -> Int {
input - 1
}
func forward(_ forward: Bool) -> (Int) -> Int {
forward ? next : previous
}
forward(true) (3) // 4
forward(false)(3) // 2
- 返回值是函数类型的函数，叫做高阶函数(Higher-OrderFunction)
typealias 取别名
typealias用来给类型起别名
typealias Byte = Int8
typealias Short = Int16
typealias Long = Int64
typealias Date = (year: Int, month: Int, day: Int)
func test(_ date: Date) {
print(date.0)
print(date.year)
}
test((2011, 9, 10))
按照Swift标准库的定义，void就是空元组(）
public typealias Void = ()
typealias IntFn = (Int, Int) -> Int
func difference(v1: Int, v2: Int) -> Int {
v1 - v2
}
let fn: IntFn = difference
fn(20, 10) // 10
func setFn(_ fn: IntFn) { }
setFn(difference)
func getFn() -> IntFn { difference }
嵌套函数
- 将函数定义在西数内部
func forward(_ forward: Bool) -> (Int) -> Int { func next(_ input: Int) -> Int { input + 1 } func previous (_ input: Int) -> Int { input - 1 } return forward ? next : previous } forward(true)(3) // 4 forward(false)(3) // 2
inline内联函数
//水远不会被内联（即使开启了编译器优化）
@inline(never) func test() {
print("test")
}
//开启编译器优化后，即使代码很长，也会被内联（遊归调用两数、动态派发的函數除外）
@inline(__always) func test() {
print("test")
}
- 在Release模式下，编译器已经开启优化，会自动决定哪些西数需要内联，因此没必要使用
@inline