RSSReaderExample.swift

/*:
# Swift Protocol Generics

In reference to [Secret Projects Diary #2: Swift 2.0 Protocols](http://inessential.com/2015/07/19/secret_projects_diary_2_swift_2_0_prot):

An variable of type `[Feed]` means that it could have a `LocalFeed` and a `FeedlyFeed`, which may be intentional, but i think not in this case. I am assuming that the `FeedlyFolder` could be typed as `[FeedlyFeed]`. If that is the case, making the Folder protocol be generic with a constraint of Feed should do the trick.
*/

import Cocoa

protocol Feed: Equatable {
  var url: String {get}
}

func ==<T: Feed>(lhs: T, rhs: T) -> Bool {
  return lhs.url == rhs.url
}

protocol Folder {
  typealias FeedType: Feed
  
  var feeds: [FeedType] {get}
  func addFeeds(feedsToAdd: [FeedType])
}

class LocalFeed: Feed {
  var url: String
  
  init(url: String) {
    self.url = url
  }
}

class LocalFolder: Folder {
  var feeds = [LocalFeed]()
  
  func addFeeds(feedsToAdd: [LocalFeed]) {
    for oneFeed in feedsToAdd {
      if !feeds.contains(oneFeed) {
        feeds += [oneFeed]
      }
    }
  }
}


let folder = LocalFolder()
folder.addFeeds([LocalFeed(url: "Asdf"), LocalFeed(url: "123")])
folder.addFeeds([LocalFeed(url: "123"), LocalFeed(url: "xyz")])
folder.feeds