Are you getting you collections for the backend in an unexpected way? Sometimes as an array and other times as dictionary? This gist tries to solve that.

GenericDecoders.swift

extension String : CodingKey {
  public var stringValue: String {
    return self
  }
  public init?(stringValue: String) {
    self.init(stringLiteral: stringValue)
  }
  public var intValue: Int? {
    return nil
  }
  public init?(intValue: Int) {
    return nil
  }
}

//MARK: Decoder -

public func decodeModel<T>(from decoder: Decoder) throws -> T? where T: Decodable {
  let object = try T(from: decoder)
  return object
}

public func decodeArray<T>(type: [T].Type, from decoder: Decoder, key : String? = nil) throws -> [T]? where T: Decodable {
  if let aKey = key {
    let container = try decoder.container(keyedBy: String.self)
    debugPrint(container.allKeys)
    let array : [T] = try container.decode(type, forKey:aKey)
    return array
  }
  
  let array : [T] = try [T].init(from: decoder)
  return array
}

public func decodeDictionary<T>(type: [String : T].Type, from decoder: Decoder, key : String? = nil) throws -> [T]? where T: Decodable {
  
  if let aKey = key {
    let container = try decoder.container(keyedBy: String.self)
    debugPrint(container.allKeys)
    let dict = try container.decode(type, forKey:aKey)
    var allItems : [T] = [T]()
    for (_, item) in dict {
      allItems.append(item)
    }
    return allItems
  }
  
  let dict : [String : T] = try [String : T].init(from: decoder)
  var alItems : [T] = [T]()
  for (_, item) in dict {
    alItems.append(item)
  }
  return alItems
}

public func decodeCollection<T>(type: T.Type, from decoder: Decoder, key : String? = nil) throws -> [T]? where T: Decodable {
  var alItems : [T]? = nil
  
  //first try with array
  do {
    try alItems = decodeArray(type: [T].self, from: decoder, key: key)
    print(alItems ?? "no items")
  } catch {
    debugPrint(error)
  }
  
  //if we got no items
  guard alItems != nil else {
    //try with dictionary
    do {
      try alItems = decodeDictionary(type: [String : T].self, from: decoder, key: key)
      print(alItems ?? "no items")
    } catch {
      debugPrint(error)
    }
    
    return alItems
  }
  
  return alItems
}