1.字面量
常见字面量的默认类型有：
ppublic typealias IntegerLiteralType = Int
ppublic typealias FloatLiteralType = Double
ppublic typealias BooleanLiteralType = Bool
ppublic typealias StringLiteralType = String
例子：
var num = 10
var name = "wwj"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 p Optional : ExpressibleByNilLiteral
3.字面量协议应用
struct literalDemo{
var x = 0.0
var y = 0.0
}
extension literalDemo: 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 d1: literalDemo = [2.0,3.0]
print(d1.x,d1.y)
var d2: literalDemo = ["x":4.0,"y":5.0]
print(d2.x,d2.y)
