Using Unsafe pointers to manipulate a JSON Encoder

Using Swift
2

What Encoder and Decoder are you working with here? JSONEncoder provided by Foundation, or your own?

If this is for JSONEncoder/JSONDecoder, manipulating the underlying storage directly is... not supported, at best. If we ever rename the storage and container variables, your code will crash when getting decoderMirror.descendent("storage", "containers")!

A better way to do (until we add something like Unevaluated) would be to define an enum which can represent a JSON hierarchy and to encode and decode self through that:

enum JSON : Codable {
    case null
    case number(NSNumber)
    case string(String)
    case array([JSON])
    case dictionary([String : JSON])

    // define initializers taking the above and recursively converting to JSONs if necessary
    // define init(from:) and encode(to:) to write to a single-value container
}

Using that you can then encode and decode any arbitrary JSON payload and get it back as a strongly-typed JSON enum which you can inspect or vend elsewhere, without the need for accessing private implementation details.