Swift 2.0 Protocols & Generic Constraints in response to http://inessential.com/2015/07/19/secret_projects_diary_2_swift_2_0_prot

RSSReaderExample2.swift

// In the previous version https://gist.github.com/cfilipov/c9929dcb2cffcbf52a22, LocalFeed could only contain one type of Feed, this one allows it to store any feed type.

import Cocoa

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

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

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

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

struct AnyFeed: Feed {
    var url: String
    init<FeedType: Feed>(_ feed: FeedType) {
        self.url = feed.url
    }
}

class LocalFolder: Folder {
    var feeds = [AnyFeed]()
    func addFeeds<F: Feed>(feedsToAdd: [F]) {
        for f in feedsToAdd {
            let oneFeed = AnyFeed(f)
            if !feeds.contains(oneFeed) {
                feeds += [oneFeed]
            }
        }
    }
}

let localFeed = LocalFeed(url: "example.com")
let folder = LocalFolder()
folder.addFeeds([localFeed])