Swift 字面量、模式匹配、条件编译

1. 字面量

2. 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的模式有：

• 通配模式

_ 匹配任何值
_? 匹配非nil值

• 标识符模式
• 值绑定模式
• 元组模式
• 枚举case模式
  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("[0,9]")
}

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

let points = [(1, 0),(2, 2),(3, 0)]

for case let (x, 0) in points{
    print("(\(x), 0)")
}
//(1, 0)
//(3, 0)


for case let (x, y) in points{
    print("(\(x), (\(y))")
}
//(1, 0)
//(2, 2)
//(3, 0)

• 可选模式

let dogAge : Any? = 10

switch dogAge{
    case  is Int:
     print("n is Int")
    default: break
}

switch dogAge{
case let n as Int:
    print("\(n) is Int")
    default: break
}

• 表达式模式

let point = (1, 2)

switch point{
    case (0, 0):
        print("origin point");
    case(-2...3, 1...3):
        print(point)
    default:
        break
}

自定义表达模式：可以通过重载运算符，自定义表达式模式的匹配规则

class Student {
    var score = 0, name = ""
    //pattern: case 后面的内容
    //value : switch 后面的内容
    static func ~= (pattern: Int, value: Student) -> Bool{
        value.score >= pattern
    }
    static func ~= (pattern: ClosedRange<Int>, value: Student) -> Bool{
        pattern.contains(value.score)
    }

    init(score: Int, name: String) {
        self.score = score
        self.name = name
    }
}
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
}

var info = (Student(score: 50, name: "Jack"),"及格")

switch info{
    case let (60, text):
        print(text)
    default:
        print("不及格")
        break
}

3. 条件编译

//操作系统：macOS/iOS/tvOS/watchOS/Linux/Linux/Android/Windows/FreeDSB
#if os(macOS)

//CPUJ架构 arch(x86_64) || arch(arm64)
#elseif arch(x86_64)

//swift版本
#elseif swift(<5)&&swift(>=3)

//模拟器
#elseif targetEnvironment(simulator)

//可导入某模块
#elseif canImport(Foundation)

#else

#endif

自定义条件编译

image.png

// 自定义条件编译
#if DEBUG
print("1")

#endif

// 自定义条件编译
#if isTest
print("2")
#else
print("22")
#endif

#if TEST
print("3")
#else
print("33")
#endif```