字面量

常见字面量的默认类型

常见字面量的默认类型.png

可以通过typealias修改字面量的默认类型

public typealias IntegerLiteralType = Int
public typealias FloadLiteralType = Float

swift自带类型之所以能够通过字面量初始化 是因为他们遵守了对应的协议

字面量遵守的协议.png

字面量的应用

extension Int: ExpressibleByBooleanLiteral {
    public init(booleanLiteral value: Bool) {
        self = value ? 1 : 0
    }
}

var num: Int = true
print(num)

1

extension Int: ExpressibleByStringLiteral {
    public init(stringLiteral value: String) {
        self = Int(value) ?? 0
    }
}

var ma: Int = "dadad"
print(ma)

0

//CustomStringConvertible  描述协议
class Student: ExpressibleByIntegerLiteral,ExpressibleByFloatLiteral,ExpressibleByStringLiteral,CustomStringConvertible {
    
    var name: String = ""
    var score: Double = 0
    required init(floatLiteral value: Double) {
        self.score = 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
    }
    required init(integerLiteral value: Int) {
        self.score = Double(value)
    }
    var description: String {
        return "name = \(name),score=\(score)"
    }
}

var stu: Student = 90
print(stu)
stu = 98.5
print(stu)

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)
p = ["x": 11,"y": 22]
print(p)

Point(x: 10.5, y: 20.5)
Point(x: 11.0, y: 22.0)