我可以使用swift下标来处理作为字典的结构的附加功能吗?

我有一个结构叫做 DailyEvents 它初始化为字典。但是,我们试图在另一个类中附加到字典,收到错误:

不能使用不可变值上的突变成员,因为Advvices是GET唯一属性。

下面是我们尝试使用struct和append的函数:

DispatchQueue.main.async {
   self.carePlanManager.store.enumerateEvents(of: ockActivity, startDate: self.startDate as DateComponents, endDate: self.endDate as DateComponents, handler: { (event, _) in
        if let event = event {
            self.dailyEvents?.allEvents.append(event)
        }
    }, completion: { (_, _) in
        innersemaphore.signal()
    })
}

以下是结构的定义:

struct DailyEvents {
    // MARK: Properties

    private var mappedEvents: [NSDateComponents: [OCKCarePlanEvent]]

    var allEvents: [OCKCarePlanEvent] {
        return Array(mappedEvents.values.flatMap{$0})
    }

    var allDays: [NSDateComponents] {
        return Array(mappedEvents.keys)
    }

    subscript(day: NSDateComponents) -> [OCKCarePlanEvent] {
        get {
            if let events = mappedEvents[day] {
                return events
            }
            else {
                return []
            }
        }

        set(newValue) {
            mappedEvents[day] = newValue
        }
    }

    // MARK: Initialization

    init() {
        mappedEvents = [:]
    }
}

我以为下标负责查询或附加到数据结构的功能,但它没有。我应该直接在dailyevents结构中创建一个附加函数吗?