断言

// 断言

// assert(<#T##condition: Bool##Bool#>, <#T##message: String##String#>)

// 断言在debug期间才会执行，编译期间不会打包进去

private let absoluteZeroInCelsius = -172.0

func convetToKelvin(_ celsius: Double) -> Double {

assert(celsius > absoluteZeroInCelsius, "输入的摄氏温度不能低于决定零度")

return celsius - absoluteZeroInCelsius

}

let roomTeperature = convetToKelvin(27)

// 编译就报错了，

let tooCold = convetToKelvin(-300)