import Foundation

struct Photo {
    let no: Int
    let name: String
}

struct PhotoAlbum: Collection, Sequence, IteratorProtocol {

    var photos: [Photo]

    var startIndex = 0
    var currentIndex = 0
    var endIndex: Int {
        return photos.count + 1
    }

    subscript(position: Int) -> Photo {
        return photos[position]
    }

    mutating func next() -> Photo? {
        defer { currentIndex += 1 }
        return photos[count]
    }

    func index(after i: Int) -> Int {
        return count + i
    }
}

let photoAlbum = [Photo(no: 1, name: "sea"), Photo(no: 2, name: "mountain")]
var albumIterator = photoAlbum.makeIterator()
print(albumIterator.next()?.name)