Two approached to a Swift enum with associated type

ScriptMessageEnum.swift

// Enum with manual parsing.
enum ScriptMessage {
    case registerForRemoteNotifications
    case showBackButton(url: URL)
    case signOutCompleted

    init?(body: [String: Any]) {
        switch body["name"] as? String {
        case "registerForRemoteNotifications":
            self = .registerForRemoteNotifications
        case "showBackButton":
            guard
                let urlString = body["url"] as? String,
                let url = URL(string: urlString)
            else { return nil }
            self = .showBackButton(url: url)
        case "signOutCompleted":
            self = .signOutCompleted
        default:
            return nil
        }
    }
}

ScriptMessageNestedEnum.swift

class ScriptMessage {
    let name: Name
    let data: [String: Any]?

    init?(message: WKScriptMessage) {
        guard
            let body = message.body as? [String: Any],
            let rawName = body["name"] as? String,
            let name = Name(rawValue: rawName)
        else { return nil }

        self.name = name
        self.data = body["data"] as? [String: Any]
    }
}

extension ScriptMessage {
    enum Name: String {
        case registerForRemoteNotifications
        case showBackButton
        case signOutCompleted
    }

    var url: URL? {
        switch name {
        case .showBackButton:
            let rawURL = data?["url"] as? String ?? ""
            return URL(string: rawURL)
        default:
            return nil
        }
    }
}