Swift 系统学习 20 结构体 添加可失败的构造方法

//: Playground - noun: a place where people can playimport UIKit/* * 本节主要内容: * 1.添加可失败的构造方法 */struct LocationNew {    var latitude: Double  = 0.0    var longitude: Double = 0.0    // 添加可选型属性    var placeName: String? // nil        // 假定参数格式: "39.123,116.456"    // 错误参数格式: "39.123*116.456"//    init?(coordinateString: String) {//        // 获取子字符串//        if let commaRange = coordinateString.range(of: ",") {//            // 1.获取逗号所在的index//            let commaIndex = coordinateString.index(commaRange.lowerBound, offsetBy: 0)//            // 2.subString to获取纬度//            if let firstElement = Double(coordinateString.substring(to: commaIndex)) {//                // 3.subString from获取经度//                if let secondElement = Double(coordinateString.substring(from: coordinateString.index(commaIndex, offsetBy: 1))) {//                    // 经纬度都可以获取//                    latitude  = firstElement//                    longitude = secondElement//                } else {//                    // 获取经度失败//                    return nil//                }//            } else {//                // 获取纬度失败//                return nil//            }//        } else {//            // 无法获取逗号的index//            return nil//        }//    }        // guard语句来优化上面的代码    init?(coordinateString: String) {        // 获取子字符串        guard let commaRange = coordinateString.range(of: ",") else {            return nil        }        // 1.获取逗号所在的index        let commaIndex = coordinateString.index(commaRange.lowerBound, offsetBy: 0)        // 2.subString to获取纬度        guard let firstElement = Double(coordinateString.substring(to: commaIndex)) else {            return nil        }        // 3.subString from获取经度        guard let secondElement = Double(coordinateString.substring(from: coordinateString.index(commaIndex, offsetBy: 1))) else {            return nil        }        // 经纬度都可以获取        latitude  = firstElement        longitude = secondElement    }    init(latitude: Double, longitude: Double) {        self.latitude  = latitude        self.longitude = longitude    }        init() {        latitude  = 0.0        longitude = 0.0    }        // 再加一个构造方法: 包含所有属性(推荐)    init(latitude: Double, longitude: Double, placeName: String) {        self.latitude  = latitude        self.longitude = longitude        self.placeName = placeName    }        // 自定义方法    func isNorth() -> Bool {        return latitude > 0.0    }    func isSouth() -> Bool {        return !isNorth()    }    // 模拟计算两个点的距离    func distanceTo(location: LocationNew) -> Double {        return sqrt(pow((self.latitude - location.latitude), 2) + pow((self.longitude - location.longitude), 2))    }}// 实例化, 调用可失败的构造方法// init?本质就是返回LocationNew?// location和locationNew都是LocationNew?类型var location = LocationNew(coordinateString: "39.34,122.3535")var locationNew = LocationNew(coordinateString: "23.34,122.3535")locationNew?.isNorth()locationNew?.distanceTo(location: location!)