Value-mapping-using-custom-operators.swift

import Foundation

/// operator declaration
infix operator <-

/// Maps right instance to left if of same type
///
/// - Parameters:
///   - left: optional instance to be mapped
///   - right: optional mapping value
func <- <T>(left: inout T?, right: Any?) {
  if right != nil {
    left = right as? T
  } else {
    ()
  }
}

// Maps right instance to left if of same type
//
// - Parameters:
///   - left: optional instance to be mapped
///   - right: optional mapping value
func <- <T: RawRepresentable>(left: inout T?, right: Any?) {
  if let right = right as? T {
    left = right
    return
  }
  if let right = right as? T.RawValue {
    left = T(rawValue: right)
  } else {
    ()
  }
}

// MARK:- Example

/// Gender enumeration
enum Gender: String {
  
  case male
  case female
  case lgbt
}

/// Person structure containing name, age and gender
struct Person {
  
  var firstName: String?
  var lastName: String?
  var age: Int?
  var gender: Gender?
  
  init(dictionary: [String : Any]) {
    firstName <- dictionary["firstName"]
    lastName <- dictionary["lastName"]
    age <- dictionary["age"]
    gender <- dictionary["gender"]
  }
}