JsonParser

Json.swift

struct Error : ErrorType {
  let message: String
}

struct Json {
  let dictionary: [String : AnyObject]
  
  init?(dictionary: [String : AnyObject]?) {
    guard let dictionary = dictionary else { return nil }
    self.dictionary = dictionary
  }
  
  func get<T, U>(key: String, transformer: T -> U?) throws -> U {
    let gotOptional = dictionary[key]
    
    guard let got = gotOptional else { throw Error(message: "Key: \(key) is not found.") }
      
    guard let typed = got as? T else { throw Error(message: "Key: \(key) was wrong type. Value is \(got)") }
      
    guard let transformed = transformer(typed) else { throw Error(message: "Key: \(key), Value: \(typed) cannot be transformed") }
      
    return transformed
  }
  
  func get<T>(key: String) throws -> T {
    return try get(key, transformer: { $0 as T })
  }
  
  func getOptional<T, U>(key: String, transformer: T -> U?) throws -> U? {
    let gotOptional = dictionary[key]
    guard let got = gotOptional else { return nil }
    
    guard let typed = got as? T else { throw Error(message: "Key: \(key) was wrong type. Value is \(got)") }
    
    guard let transformed = transformer(typed) else { throw Error(message: "Key: \(key), Value: \(typed) cannot be transformed") }
    
    return transformed
  }
  
  func getOptional<T>(key: String) -> T? {
    do {
      return try getOptional(key, transformer: { $0 as T })
    } catch {
      return nil
    }
  }
  
  func getArray<T, U>(key: String, transformer: T -> U?) throws -> [U] {
    let got: [T] = try get(key)
    return got.flatMap(transformer)
  }
  
}

enum Gender: String {
    case Male = "M"
    case Female = "F"
}

struct Dog {
    let name: String
}

struct Person {
  let name: String
  let age: Int
  let gender: Gender
  let dogs: [Dog]
  let optional: String?
  
  init?(dictionary: [String: AnyObject]?) {
    guard let dictionary = dictionary, json = Json(dictionary: dictionary) else { return nil }
    do {
      name = try json.get("name")
      age = try json.get("age")
      gender = try json.get("gender") { Gender(rawValue: $0) }
      dogs = try json.getArray("dogs") { Dog(name: $0) }
      optional = json.getOptional("foo")
    } catch let error {
      print(error)
      return nil
    }
  }
}

var jsonDict = [String: AnyObject]()

jsonDict["name"] = "Adam" as? AnyObject
jsonDict["age"] = 32 as? AnyObject
jsonDict["gender"] = "M" as? AnyObject
jsonDict["dogs"] = ["Robert", "Fido", "Zolo"] as? AnyObject
print(jsonDict)

let person = Person(dictionary: jsonDict)
if let person = person {
  print(person.name)
  print(person.age)
  print(person.gender)
  print(person.dogs)
  print(person.optional)
}