KeyPath

KeyPathBinding.swift

// ------------------------------------
// Network
// ------------------------------------

struct MeetupResponse {
  var groupName: String = ""
  var groupOrganizers: [String] = []
  var meetupTitle: String = ""
  var meetupAttendes: Int = 0
  var meetupSpeakers: [String]? = nil
}

// ------------------------------------
// Domain
// ------------------------------------

struct MeetupGroup {
  var name: String = ""
  var organizers: [String] = []
  var event: MeetupEvent = MeetupEvent()
}

struct MeetupEvent {
  var title: String = ""
  var attendes: Int = 0
  var speakers: [String]? = nil
}

// ------------------------------------
// Binding
// ------------------------------------

struct Binding<L, R> {
  var left: (L, R) -> L
  var right: (R, L) -> R
  init<V>(_ left: WritableKeyPath<L, V>, _ right: WritableKeyPath<R, V>){
    self.left = { l, r in
      var lx = l
      lx[keyPath: left] = r[keyPath: right]
      return lx
    }
    self.right = { r, l in
      var rx = r
      rx[keyPath: right] = l[keyPath: left]
      return rx
    }
  }
}

// ------------------------------------
// Binding operator
// ------------------------------------

precedencegroup BindGroup {}
infix operator ~ : BindGroup

func ~ <L, R, V>(lhs:  WritableKeyPath<L, V>, rhs: WritableKeyPath<R, V>) -> Binding<L, R> {
  return Binding(lhs, rhs)
}

// ------------------------------------
// Binding
// ------------------------------------

let bindings = [
  \MeetupResponse.groupOrganizers ~ \MeetupGroup.organizers,
  \.groupName ~ \.name,
  \.meetupTitle ~ \.event.title,
  \.meetupAttendes ~ \.event.attendes,
  \.meetupSpeakers ~ \.event.speakers
]

// ------------------------------------
// Map from Response to Domain and back
// ------------------------------------

var r = MeetupResponse()
r.groupName = "group"
r.groupOrganizers = ["a", "b"]
r.meetupTitle = "Meetup title"
r.meetupAttendes = 12
r.meetupSpeakers = ["1", "2"]

let meetup = bindings.reduce(MeetupGroup()) { group, binding in binding.right(group, r) }
let meetupResponse = bindings.reduce(MeetupResponse()) { group, binding in binding.left(group, meetup) }

print(meetupResponse)