Extension of the restricted vocabulary protocol

I am trying to get a specific type of dictionary to conform to the protocol.

typealias FirebaseDictionary = Dictionary<String, FirebaseValue>

      

        
        
        
      

    

I would like to comply with the protocol FirebaseValue

protocol FirebaseValue {
    // stuff here
}

      

        
        
        
      

    

I tried this

extension FirebaseDictionary: FirebaseValue {

}

      

        
        
        
      

    

but I got an error Constrained extension must be declared on the unspecialized generic type 'Dictionary' with constraints specified by a 'where' clause

. So now I have this

extension Dictionary where Key == String, Value == FirebaseValue {

}

      

        
        
        
      

    

but I can't seem to figure out the correct syntax to make this conform to the protocol, if at all possible. If not possible, is there any other way to achieve the same effect? I'm trying to only allow certain types in a property and it's easy to distinguish what type they are when reading.

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