Alternate take on the sequence protocol using AnyGenerator. See http://stackoverflow.com/a/26219833/558735

gistfile1.txt

// paste this into a playground

import Foundation

class Car {
    var name : String
    init(name : String) {
        self.name = name
    }
}

class Cars : SequenceType {
    var carList = [Car]()
    
    func generate() -> AnyGenerator<Car> {
        // keep the index of the next car in the iteration
        var nextIndex = 0
        
        // Construct a AnyGenerator<Car> instance, passing a closure that returns the next car in the iteration
        return anyGenerator({ [weak self] in
            guard let car = self?.carList.get(nextIndex) else
            {
                return nil
            }
            
            nextIndex += 1
            return car
        })
    }
}

extension Array
{
    func get(index: Int) -> Element? {
        guard index >= 0 && index < self.count else {
            return nil
        }
        
        return self[index]
    }
}

let cars = Cars()

cars.carList.append(Car(name: "Honda"))
cars.carList.append(Car(name: "Toyota"))

for car in cars {
    debugPrint(car.name)
}