Subscript: access my dictionary values with a String enumeration

Question

I want to do something like that: access my dictionary values with a String enumeration. I am trying to overload the subscript of the dictionary but without success.

Answer 1

The simplest approach is to just lift the dictionary into more context. The context in this case is "it only has keys from this enum." Lifting a type in Swift is very straightforward. Just wrap it in a struct.

// This could be a nested type inside JSONObject if you wanted.
enum JSONKeys: String {
    case district
}

// Here's my JSONObject. It's much more type-safe than the dictionary,
// and it's trivial to add methods to it.
struct JSONObject {
    let json: [String: AnyObject]
    init(_ json: [String: AnyObject]) {
        self.json = json
    }

    // You of course could make this generic if you wanted so that it
    // didn't have to be exactly JSONKeys. And of course you could add
    // a setter.
    subscript(key: JSONKeys) -> AnyObject? {
        return json[key.rawValue]
    }
}

let address: [String: AnyObject] = ["district": "Bob"]

// Now it's easy to lift our dictionary into a "JSONObject"
let json = JSONObject(address)

// And you don't even need to include the type. Just the key.
let district = json[.district]