Json model vs Domain model

gistfile1.swift

/* Domain model */

// A Profile consists of a person name and an optional avatar
struct Profile {
  let personName: PersonName
  let avatarURL: NSURL?
}


// These are the UX rules for showing a greeting:

// 1. When last name is available, greeting should be: "Hello John Smith."
// 2. When only first name is available, greeting should be: "Hi John!"
enum PersonName {
  case FirstName(String)
  case FullName(String, String)

  var greeting: String {
    switch self {
    case .FirstName(let first):
      return "Hi \(first)!"
    case .FullName(let first, let last):
      return "Hello \(first) \(last)."
    }
  }
}


/* Json model */

// This is the json data returned by an API.
// The `profile` property maps this json to the domain model.
// It contains all the custom logic supplied by the API developers.
//
// Example JSON:
// {
//   "FirstName": "Tom",
//   "AvatarURL": "http://example.com",
//   "UseAvatar: false
// }
//
// The JSON parser for this type is generated by swift-json-gen.
struct ProfileJson {
  let FirstName: String
  let LastName: String?
  let UseAvatar: Bool
  let AvatarUrl: String?

  var profile: Profile {
    // These are the business rules for handeling the JSON data:
    // 1. FirstName is always available
    // 2. LastName is sometimes available
    // 3. When UseAvatar == false, ignore the url
    // 4. If AvatarUrl is not a real url, ignore it

    let name: PersonName
    if let last = LastName {
      name = PersonName.FullName(FirstName, last)
    }
    else {
      name = PersonName.FirstName(FirstName)
    }

    let avatarURL: NSURL?
    if let url = AvatarUrl where UseAvatar {
      avatarURL = NSURL(string: url)
    }
    else {
      avatarURL = nil
    }

    return Profile(personName: name, avatarURL: avatarURL)
  }
}

Accompanying blog post: Swift + JSON with code generation