21-字面量

//字面量1-4
//1.字面量,10,false,"Jack"都是字面量
//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"
//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,只需知道就行一般不这么做
typealias FloatLiteralType = Float
typealias IntegerLiteralType = UInt8
var age0 = 10
var height0 = 1.68

//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
 Bool:ExpressibleByBooleanLiteral
 Int:ExpressibleByIntegerLiteral
 Float、Double:ExpressibleByIntegerLiteral、ExpressibleByFloatLiteral
 Dictionary:ExpressibleByDictionaryLiteral
 String:ExpressibleByStringLiteral
 Array、Set:ExpressibleByArrayLiteral
 Optional:ExpressibleByNilLiteral
 */
var b: Bool = false //ExpressibleByBooleanLiteral
var i: Int = 10 //ExpressibleByIntegerLiteral
var f0: Float = 10 //ExpressibleByIntegerLiteral
var f1: Double = 10.0 //ExpressibleByBooleanLiteral
var d0: Float = 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：Person对象能不像Int一样用字面量那样初始化呢？可以遵循字面量协议即可
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) { //ExpressibleByStringLiteral遵循了3个协议
        self.name = value
    }
    required init(unicodeScalarLiteral value: String) { //特殊字符🐂
        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

//4.字面量协议应用
struct Point {
    var x = 0.0, y = 0.0
}
extension Point : ExpressibleByArrayLiteral, ExpressibleByDictionaryLiteral {
    init(arrayLiteral elements: Float...) { //...表示不确定个数
        guard elements.count > 0 else { return }
        self.x = elements[0]
        guard elements.count > 1 else { return }
        self.y = elements[1]
    }
    init(dictionaryLiteral elements: (String, Float)...) {
        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)