SwiftExtension扩展得使用详细介绍

extension Double {
    var km: Double {
        self * 1_000.0
    }
    var m: Double {
        self
    }
    var dm: Double {
        self / 100.0
    }
    var cm: Double {
        self / 10.0
    }
    var mm: Double {
        self / 1_000.0
    }
}
var d = 100.0
d.km
d.m
d.dm

var arr: Array<Int> = [10, 20, 30]
extension Array {
    subscript(nullable idx: Int) -> Element? {
        if (startIndex ..< endIndex).contains(idx) {
            return self[idx]
        }
        return nil
    }
}
print(arr[nullable: 1] ?? 0)

extension Int {
    func repeats(task: () -> Void) {
        for _ in 0..<self {
            task()
        }
    }
    enum Kind {
        case negative, zero, positive
    }
    var kind: Kind {
        switch self {
        case 0: return .zero
        case let x where x > 0: return.positive
        default: return .negative
        }
    }
    subscript(digitIndex: Int) -> Int {
        var decimalBase = 1
        for _ in 0..<digitIndex {
            decimalBase *= 10
        }
        return (self / decimalBase) % 10
    }
}

class Person {
    var age: Int
    var name: String
    init(age: Int, name: String) {
        self.age = age
        self.name = name
    }
}
extension Person: Equatable {
    static func == (left: Person, right: Person) -> Bool {
        left.age == right.age && left.name == right.name
    }
    convenience init() {
        self.init(age: 0, name: "")
    }
}

struct Point {
    var x: Int = 0
    var y: Int = 0
}
extension Point {
    init(_ point: Point) {
        self.init(x: point.x, y: point.y)
    }
}

extension BinaryInteger {
    func isOdd() -> Bool {
        self % 2 != 0
    }
}

protocol TestProtocol {
    func test1()
}
extension TestProtocol {
    func test1() {
        print("TestProtocol test1")
    }
    func test2() {
        print("TestProtocol test2")
    }
}
class TestClass: TestProtocol {
    func test1() {
        print("TestClass test1")
    }
    func test2() {
        print("TestClass test2")
    }
}
var cls: TestProtocol = TestClass()
cls.test1() //TestClass test1
cls.test2() //TestProtocol test2

extension Stack: Equatable where E: Equatable {
}