模式（Pattern）

• 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\guard\while\for语句的条件等

• Swift中的模式有

• 通配符模式(Wildcard Pattern)
• 标识符模式(Identifier Pattern)
• 值绑定模式(Value-Binding Pattern)
• 元组模式(Tuple Pattern)
• 枚举Case模式(Enumeration Case Pattern)
• 可选模式(Optional Pattern)
• 类型转换模式(Type-Casting Pattern)
• 表达式模式(Expression Pattern)

通配符模式（Wildcard Pattern）

• 匹配任何值
• _?匹配非nil值

enum Life {
    case human(name: String, age: Int?)
    case animal(name: String, age: Int?)
}

func check(_ life: Life) {
    switch life {
    case .human(let name, _):
        print("human", name)
    case .animal(let name, _?):
        print("animal", name)
    default:
        print("other")
    }
}

check(.human(name: "Rose", age: 20))
check(.human(name: "Jack", age: nil))
check(.animal(name: "Dog", age: 5))
check(.animal(name: "Cat", age: nil))
/*
 human Rose
 human Jack
 animal Dog
 other
 */

标识符模式（Identifier Pattern）

• 给对应的变量、常量名赋值

var age = 10
let name = "jack"

值绑定模式（Value-Binding Pattern）

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

元组模式（Tuple Pattern）

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

let name: String? = "Jack"
let age = 18
let info: Any = [1, 2]
switch (name, age, info) {
case (_?, _, _ as String):
    print("case")
default:
    print("default")
} // default

var scores = ["Jack" : 98, "Rose" : 100, "Kate" : 86]
for (name, score) in scores {
    print(name, score)
}

枚举Case模式（Enumeration Case Pattern）

• if case的语句等价于只有1个case的switch语句

let age = 2
// 原来的写法
if age >= 0 && age <= 9 {
    print("[0, 9]")
}
// 枚举Case模式
if case 0...9 = age {
    print("[0, 9]")
}
guard case 0...9 = age else { return }
print("[0, 9]")

switch age {
case 0...9: print("[0, 9]")
default: break
}

let ages: [Int?] = [2, 3, nil, 5]
for case nil in ages {
    print("有nil值")
    break
} // 有nil值

let points = [(1, 0), (2, 1), (3, 0)]
for case let (x, 0) in points {
    print(x)
} // 1 3

可选模式（Optional Pattern）

let age: Int? = 42
if case .some(let x) = age { print(x) }
if case let x? = age { print(x) }

let ages: [Int?] = [nil, 2, 3, nil, 5]
for case let age? in ages {
    print(age)
} // 2 3 5

let ages: [Int?] = [nil, 2, 3, nil, 5]
for item in ages {
    if let age = item {
        print(age)
    }
} // 2 3 5

func check(_ num: Int?) {
    switch num {
    case 2?: print("2")
    case 4?: print("4")
    case 6?: print("6")
    case _?: print("other")
    case _: print("nil")
    }
}
check(4) // 4
check(8) // other
check(nil) // nil

类型转换模式（Type-Casting Pattern）

let num: Any = 6
switch num {
case is Int:
    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")}}
class Dog: Animal { func run() { print(type(of: self), "run")}}
class Cat: Animal { func jump() { print(type(of: self), "jump")}}
func check(_ animal: Animal) {
    switch animal {
    case let dog as Dog:
        dog.eat()
        dog.run()
    case is Cat:
        animal.eat()
    default: break
    }
}
// Dog eat
// Dog run
check(Dog())
// Cat eat
check(Cat())

表达式模式（Expression Pattern）

• 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.

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

extension String {
    static func ~= (pattern: (String) -> Bool, value: String) -> Bool {
        pattern(value)
    }
}

func hasPrefix(_ prefix: String) -> ((String) -> Bool) { { $0.hasPrefix(prefix)} }
func hasSuffix(_ suffix: String) -> ((String) -> Bool) { { $0.hasSuffix(suffix)} }

var str = "jack"
switch str {
case hasPrefix("j"), hasSuffix("k"):
    print("以j开头，以k结尾")
default: break
} // 以j开头，以k结尾

func isEven(_ i: Int) -> Bool { i % 2 == 0}
func isOdd(_ i: Int) -> Bool { i % 2 != 0}

extension Int {
    static func ~= (pattern: (Int) -> Bool, value: Int) -> Bool {
        pattern(value)
    }
}

var age = 9
switch age {
case isEven:
    print("偶数")
default:
    print("奇数")
default:
    print("其他")
}

prefix operator ~>
prefix operator ~>=
prefix operator ~<
prefix operator ~<=
prefix func ~> (_ i: Int) -> ((Int) -> Bool) { { $0 > i } }
prefix func ~>= (_ i: Int) -> ((Int) -> Bool) { { $0 >= i } }
prefix func ~< (_ i: Int) -> ((Int) -> Bool) { { $0 < i } }
prefix func ~<= (_ i: Int) -> ((Int) -> Bool) { { $0 <= i } }

var age = 9
switch age {
case ~>=0:
    print("1")
case ~>10:
    print("2")
default: break
}

pattern: case后面的内容
value: switch后面的内容

where

• 可以使用where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
}

var ages = [10, 20, 44, 23, 55]
for age in ages where age > 30 {
    print(age)
} // 44 55

protocol Stackable { associatedtype Element }
protocol Container {
    associatedtype Stack : Stackable where Stack.Element : Equatable
}

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 { }