无法分配给 Swift 类型的不可变表达式

Question

我在没有太多帮助的情况下看到了几个类似的 SO 问题，

我正在尝试使用 timesArray 函数 updateDailyTimes 更新星期一的 availabilityTimes

availabilityTimes 和 timesArray 的示例

 var availabilityTimes = [
         "Monday": [ "available" : true,
                     "times": [
                         ["startTime": "9:00 am", "endTime": "1:30 pm" ],
                         ["startTime": "2:30 pm", "endTime": "6:00 pm" ],
                         ["startTime": "7:30 pm", "endTime": "9:00 pm" ]
                     ]
         ],
         "Tuesday": [ "available" : true,
                     "times": [
                         ["startTime": "9:00 am", "endTime": "6:00 pm" ]
                     ]
                    ]
          ]




var timesArray = [
                    ["startTime": "9:00 am", "endTime": "1:30 pm" ],
                    ["startTime": "2:30 pm", "endTime": "6:00 pm" ],
                    ["startTime": "7:30 pm", "endTime": "9:00 pm" ]
                  ]

这是我的代码，当我调用下面的函数时，我在代码行value["times"] as [[String : String]] = timesArray 中收到错误消息cannot assign to immutable expression of type [[String : String]]

func updateDailyTimes(day: String, timesArray: [[String:String]]){

    guard var updatedTimes = self.availabilityTimes as? [String: AnyObject] else{
        return
    }

    for (key, var value) in updatedTimes {

        if key == day{
            for (key1, value1) in value as! [String : AnyObject]{
                if key1 as String == "times" {
                    value["times"] as [[String : String]] = timesArray // I get an error message in this line
                }
            }

        }
    }
}

Answer 1

根据我的评论，我的意思是一个自定义结构 Times 用于开始和结束时间，一个结构 DailyTimes 具有所需的属性和一个变异函数来更新 Times 数组：

struct Times {
    let start : String
    let end : String
}

struct DailyTimes {
    let weekday : String
    var available : Bool
    var times = [Times]()

    mutating func update(times : [Times]) {
        self.times = times
    }
}

现在创建availableTimes 字典：

var availableTimes = ["Monday" : DailyTimes(weekday: "Monday", available: true, times: [Times(start: "9:00 am", end:"1:30 pm"),
                                                                                        Times(start: "2:30 pm", end:"6:00 pm"),
                                                                                        Times(start: "7:30 pm", end:"9:00 pm")]),
                      "Tuesday" : DailyTimes(weekday: "Tuesday", available: true, times: [Times(start: "9:00 am", end:"6:00 pm")])]

还有timesArray 数组：

let timesArray = [Times(start: "9:00 am", end:"1:30 pm"),
                  Times(start: "2:30 pm", end:"6:00 pm"),
                  Times(start: "7:30 pm", end:"9:00 pm")]

由于Monday 的Times 数组已经包含timesArray 的值，让我们更新Tuesday

availableTimes["Tuesday"]?.update(times:timesArray)

终于证明了

print(availableTimes["Tuesday"]?.times)

另一个改进可能是使用 DateComponents 而不是 Strings 的时代。

Answer 2

在 Swift 中，Dictionary 是一个结构体，它是一个值类型。将值类型想象成基本类型，例如 int。

如果你有这个：

int a = 0
int b = a

然后b得到a的值，它们不相同。

因此，当您遍历字典时，您的 (key, value) 对实际上并不是字典中的内容，它们只是具有相同的值。在迭代值或引用时不要改变它也很重要。这可能会导致奇怪的错误。

enum AvailabilityTimeMarker {
    case start
    case end
}
enum DayOfTheWeek: String {
    case monday = "Monday"
    case tuesday = "Tuesday"
    case wednesday = "Wednesday"
    case thursday = "Thursday"
    case friday = "Friday"
    case saturday = "Saturday"
    case sunday = "Sunday"
}

typealias Availability = [DayOfTheWeek : AvailabilityDay]
typealias AvailabilityDay = [String : Any]
typealias AvailabilityArray = [AvailabilityTime]
typealias AvailabilityTime = [AvailabilityTimeMarker : String]

var availabilityTimes: Availability = [
    .monday : [ "available" : true,
                "times": [
                    ["startTime": "9:00 am", "endTime": "1:30 pm" ],
                    ["startTime": "2:30 pm", "endTime": "6:00 pm" ],
                    ["startTime": "7:30 pm", "endTime": "9:00 pm" ]
        ]
    ],
    .tuesday : [ "available" : true,
                 "times": [
                    ["startTime": "9:00 am", "endTime": "6:00 pm" ]
        ]
    ]
]

var timesArray: AvailabilityArray = [
    [.start : "9:00 am", .end : "1:30 pm" ],
    [.start : "2:30 pm", .end : "6:00 pm" ],
    [.start : "7:30 pm", .end : "9:00 pm" ]
]

func updateDailyTimes(day: DayOfTheWeek, timesArray: AvailabilityArray) {

    let availabilities = self.availabilityTimes

    var newtimes = availabilities

    if var newDayAvailability = availabilities[day] {
        newDayAvailability["times"] = newtimes

        newtimes[day] = newDayAvailability

        self.availabilityTimes = newtimes// Since we're not using reference semantics, we have to change the entire value
    }
}