gistfile1.swift

// MARK: JSON Valid Types
protocol JSON {}

// MARK: - Type Aliases
typealias JSONDictionary = Dictionary<String, JSON>
typealias JSONArray = Array<JSON>

// MARK: - Primitives
extension Bool: JSON {}
extension Int: JSON {}
extension Double: JSON {}
extension String: JSON {}

// MARK: - Structures
extension Dictionary: JSON {}
extension Array: JSON {}

var x: Dictionary<String, JSON> = [
    "String": "0",
    "Bool": true,
    "Int": 5,
    "Arr": ["1"],
    "Dict": [
        "Arr0": ["1", "1"]
    ]
]
        
var z = (x["Dict"] as Dictionary<String, JSON>)._bridgeToObjectiveC()   // EXC_BAD_INSTRUCTION at runtime
var z = (x["Dict"]! as Dictionary<String, JSON>)._bridgeToObjectiveC() // EXC_BAD_INSTRUCTION at runtime
var z = ((x["Dict"] as Dictionary<String, JSON>) as? NSDictionary) // NSDictionary is not a subtype of Dictionary<String, JSON>