在 Swift 属性包装器中公开字典

Question

I have an internal dictionary that I don't want to expose to the user. Instead, I expose only certain values using properties, like this:

public var artist: String? {
  get {
     return items["artist"]
  }
  set {
     items["artist"] = newValue
  }
}

//...so on for another 20 or so items

As you can imagine, this ends up getting repeated quite a lot. I was thinking that property wrappers would be a nice way to clean this up - however, it's not possible to pass items directly to the wrapper, since property wrappers are created before init (so self would not be accessible).

Is there a way around this, or is this just one of the limitations of propertyWrappers?

Answer 1

You could build a generic solution. I did one, but you can probably improve it:

    class PropertyWrapper {
    
    private var items: [String: Any] = ["artist": "some dude"]
    
    enum Key: String {
        case artist
    }
    
    func getItem<T: Any>(key: Key) -> T {
        guard let item = items[key.rawValue] as? T else {
            preconditionFailure("wrong type asked for")
        }
        return item
    }
    
    func setItem(value: Any, key: Key) {
        items[key.rawValue] = value
    }
}

class GetValueClass {
    
    func getValue() {
        let wrapper = PropertyWrapper()
        let value: String = wrapper.getItem(key: .artist)
    }
}

class SetValueClass {
    
    func setValue() {
        let wrapper = PropertyWrapper()
        wrapper.setItem(value: "some", key: .artist)
    }
}