JSON 문자열을 Dictionary로 변환

let json = "{\"fuga\":\"aiueo\",\"foo\":999,\"user\":{\"name\":\"tenten0213\",\"age\":30}}"
let data = json.data(using: .utf8)!

do {
    let dic = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] // ["fuga": "aiueo", "user": ["name": "tenten0213", "age": 30], "foo": 999]
    dic?["fuga"] // "aiueo"
    let user = dic?["user"] as? [String: Any] // ["name": "tenten0213", "age": 30]
    user?["name"] as? String // "tenten0213"
    user?["age"] as? Int // 30
} catch {
    print(error.localizedDescription)
}