摘要：//let possibleNumber = "123" //let convertedNumber = Int(possibleNumber) //// convertedNumber 被推测为类型 "Int?", 或者类型 "optional Int" //因为该构造器可能会失败,所以它返回一个 阅读全文

摘要：//: Playground - noun: a place where people can play import Cocoa var str = "Hello, playground" let cat = "?";print(cat) let minVale = uint8.min let m 阅读全文