swift模式匹配

一、模式

1、什么是模式？

模式是用于匹配的规则，比如switch的case、捕捉错误的catch、if\gurad\while\for语句的条件等

2、Swift中的模式有

通配符模式、标识符模式、值绑定模式、元祖模式、枚举case模式、可选模式、类型转换模式、表达式模式。

二、模式详解

1、通配符模式

_ 匹配任何值
_? 匹配非nil值

2、标识符模式

给对应的变量、常量名赋值

var name = "rose"
let sex = "man"

3、值绑定模式

let point = (3,2)
switch point{
case let(x,y):
         print("The point is at \(x) , \(y)")
}

4、元组模式

let point = [(0,0),(1,0),(2,0)]
for (x,_) in point{
    print(x)
}

var scores = ["Jack": 98,"rose": 100,"Jim": 80]
for (name,score) in scores{
      print(name,score)
}

5、枚举Case模式（Enumeration Case Pattern）

if case 语句等价于只有一个case的switch语句

let age = 2
if case 0...9 = age{
    print("在[0,9]范围之间")
}
guard case 0...9 = age else { return }
switch age{
      case 0...9: print("在[0,9]范围之间")
default : break
}

6、可选模式（Optional Pattern）

let age: [Int?] = [nil,2,3,nil,8]
for case let age? in ages{
      print(age)
}

for item in ages{
      if let age = item {
          print(age)
      }
}

func check (_ num: Int?){
      switch num{
          case 2?: print(2)
          case 3?: print(3)
          case _?: print("other")
          case _: print("nil")
      }
}
check(4)
check(nil)

7、类型转换模式（Type-Caseing Pattern）

let num: Any = 6
switch num {
    case is Int:
    // 编译器依然认为num是Any类型
        print("is Int", num)
    //case let n as Int:
    //    print("as Int", n + 1)
    default:
    break
}

class Animal {
    func eat() {
        print(type(of: self), "eat") 
    }    
 }

8、表达式模式

表达式模式用在case中

let point = (1, 2)
switch point {
    case (0, 0):
        print("(0, 0) is at the origin.")
    case (-2...2, -2...2):
        print("(\(point.0), \(point.1)) is near the origin.")
    default:
        print("The point is at (\(point.0), \(point.1)).")    
} // (1, 2) is near the origin.

9、自定义表达式模式

可以通过重载运算符，自定义表达式模式的匹配规则。

struct Student {
var score = 0, name = ""
static func ~= (pattern: Int, value: Student) -> Bool { value.score >= pattern }
static func ~= (pattern: ClosedRange<Int>, value: Student) -> Bool { pattern.contains(value.score) } static func ~= (pattern: Range<Int>, value: Student) -> Bool { pattern.contains(value.score) }
}

var stu = Student(score: 75, name: "Jack") switch stu {
case 100: print(">= 100")
case 90: print(">= 90")
case 80..<90: print("[80, 90)") case 60...79: print("[60, 79]") case 0: print(">= 0")
default: break
} // [60, 79]
if case 60 = stu {
    print(">= 60")
} // >= 60
 var info = (Student(score: 70, name: "Jack"), "及格") switch info {
case let (60, text): print(text)
default: break
} // 及格

10、where

可以使用where作为模式匹配增加匹配条件

var data = (10, "Jack")
switch data {
        case let (age, _) where age > 10:
        print(data.1, "age>10") case let (age, _) where age > 0:
        print(data.1, "age>0") default: break
}

protocol Stackable {
    associatedtype Element
}

protocol Container {
    associatedtype Stack :
        Stackable where Stack.Element : Equatable    
}
 
var ages = [10, 20, 44, 23, 55]
for age in ages where age > 30 {
     print(age)
} // 44 55

func equal<S1: Stackable, S2: Stackable>(_ s1: S1, _ s2: S2) -> Bool where S1.Element == S2.Element, S1.Element : Hashable {
    return false
}
 
extension Container where Self.Stack.Element : Hashable {}

最后编辑于：2019.12.16 18:53:45