Swift-guard

swift 中guard具体的好处

用它避免繁杂的逻辑判断
如：
guard
let name = json["city"] as? String,
let latitude = json["latitude"] as? Double,
let longitude = json["longitude"] as? Double,
let sunriseString = json["sunrise"] as? String,
let sunsetString = json["sunset"] as? String,
let sunrise = DateFormatter.isoDateFormatter.date(from: sunriseString),
let sunset = DateFormatter.isoDateFormatter.date(from: sunsetString)
else {
fatalError("Could not instantiate a city from JSON: (json)")
}
let coordinate = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
guard CLLocationCoordinate2DIsValid(coordinate) else {
fatalError("City has invalid coordinates: (coordinate)")
}
解析字段可能失败的情况下绕过恶心的if else 嵌套,只检测不满足条件的结果处理