美文网首页
21-Swift字面量

21-Swift字面量

作者: 一抹相思泪成雨 | 来源:发表于2020-12-22 08:02 被阅读0次

    1.字面量

    • Swift自带的绝大部分类型,都支持直接通过字面量进行初始化
      • Bool、Int、Float、Double、String、Array、Dictionary、Set、Optional等
    var age = 10
    var isRed = false
    var name = "Jack"
    /// 上面代码中的10,false,"Jack"就是字面量
    
    /// 常见字面量的默认类型
    public typealias IntegerLiteralType = Int
    public typealias FloatLiteralType = Double
    public typealias BooleanLiteralType = Bool
    public typealias StringLiteralType = String
    
    /// 可以通过typealias修改字面量的默认类型
    //typealias FloatLiteralType = Float
    //typealias InterLiteralType = UInt8
    age = 10 // UInt8
    var height = 1.58 // Float
    

    2.字面量协议

    • Swift自带类型之所以能够通过字面量初始化,是因为它们遵守了对应的协议
      1. Bool : ExpressibleByBooleanLiteral
      2. Int : ExpressibleByIntegerLiteral
      3. Float、 Double : ExpressibleByIntegerLiteral、ExpressibleByFloatLiteral
      4. Dictionary : ExpressibleByDictionaryLiteral
      5. String : ExpressibleByStringLiteral
      6. Array、Set : ExpressibleByArrayLiteral
      7. Optional : ExpressibleByNilLiteral
    var b: Bool = false                     // ExpressibleByBooleanLiteral
    var i: Int = 10                         // ExpressibleByIntegerLiteral
    var f0: Float = 10                      // ExpressibleByIntegerLiteral
    var f1: Float = 10.0                    // ExpressibleByFloatLiteral
    var d0: Double = 10                     // ExpressibleByIntegerLiteral
    var d1: Double = 10.0                   // ExpressibleByFloatLiteral
    var s: String = "jack"                  // ExpressibleByStringLiteral
    var arr: Array = [1, 2, 3]              // ExpressibleByArrayLiteral
    var set: Set = [1, 2, 3]                // ExpressibleByArrayLiteral
    var dict: Dictionary = ["jack" : 60]    // ExpressibleByDictionaryLiteral
    var o: Optional<Int> = nil              // ExpressibleByNilLiteral
    

    3.字面量协议应用

    extension Int : ExpressibleByBooleanLiteral {
        public init(booleanLiteral value: Bool) { self = value ? 1 : 0 }
    }
    var num: Int = true
    print(num) // 1
    
    class Student : ExpressibleByIntegerLiteral, ExpressibleByFloatLiteral, ExpressibleByStringLiteral,CustomStringConvertible {
        var name: String = ""
        var score: Double = 0
        required init(floatLiteral value: Double) { self.score = value }
        required init(integerLiteral value: Int) { self.score = Double(value) }
        required init(stringLiteral value: String) { self.name = value }
        required init(unicodeScalarLiteral value: String) { self.name = value }
        required init(extendedGraphemeClusterLiteral value: String) { self.name = value }
        var description: String { "name=\(name),score=\(score)" }
    }
    var stu: Student = 90
    print(stu)  // name=,score=90.0
    stu = 98.5
    print(stu)  // name=,score=98.5
    stu = "Jack"
    print(stu)  // name=Jack,score=0.0
    
    struct Point {
        var x = 0.0, y = 0.0
    }
    extension Point : ExpressibleByArrayLiteral, ExpressibleByDictionaryLiteral {
        init(arrayLiteral elements: Double...) {
            guard elements.count > 0 else { return }
            self.x = elements[0]
            guard elements.count > 1 else { return }
            self.y = elements[1]
        }
        
        init(dictionaryLiteral elements: (String, Double)...) {
            for (k, v) in elements {
                if k == "x" { self.x = v }
                else if k == "y" { self.y = v }
            }
        }
    }
    var p: Point = [10.5, 20.5]
    print(p) // Point(x: 10.5, y: 20.5)
    p = ["x" : 11, "y" : 22]
    print(p) // Point(x: 11.0, y: 22.0)
    

    相关文章

      网友评论

          本文标题:21-Swift字面量

          本文链接:https://www.haomeiwen.com/subject/qhlqnktx.html