Need an explanation about my missing code output

I'm currently in learning process of C# and I need an explanation. It's probably logical and simple for someone more experienced, but I thought code should work this way and it doesn't.

I'm trying to print out all Car objects inside carArray in my Garage class with foreach loop using named iterator, but when I pass false value to GetTheCars method and enter inside else block, nothing happens. Printing array in reverse works just fine. This is the code..

Main method:

static void Main(string[] args)
    {
        Garage carLot = new Garage();

        foreach (Car c in carLot.GetTheCars(false))
        {
            Console.WriteLine("{0} is going {1} MPH", c.PetName, c.CurrentSpeed);
        }

        Console.WriteLine();

        foreach (Car c in carLot.GetTheCars(true))
        {
            Console.WriteLine("{0} is going {1} MPH", c.PetName, c.CurrentSpeed);
        }
    }

Garage class:

class Garage : IEnumerable
{
    private Car[] carArray = new Car[4];

    public Garage()
    {
        carArray[0] = new Car("Rusty", 30);
        carArray[1] = new Car("Clunker", 55);
        carArray[2] = new Car("Zippy", 30);
        carArray[3] = new Car("Fred", 30);
    }

    public IEnumerator GetEnumerator()
    {
        foreach (Car c in carArray)
        {
            yield return c;
        }
    }

    public IEnumerable GetTheCars(bool ReturnReversed)
    {
        if (ReturnReversed)
        {
            for (int i = carArray.Length; i != 0; i--)
            {
                yield return carArray[i-1];
            }
        }
        else
        {
            GetEnumerator();
        }
    }

In the book example inside the else statement, the same code is written as in GetEnumerator() method:

Book code difference:

else
{
    foreach (Car c in carArray)
    {
        yield return c;
    }
}

I thought I could reuse the code inside the GetEnumerator() method that was used in previous example of the book, but it prints out nothing. If someone could explain me why I'd be grateful, cheers and thanks in advance!

Jon Skeet
people
quotationmark

You're calling GetEnumerator in the else block, but that's not going to automatically yield anything. It would be nice if you could have something like:

// This doesn't actually work!
yield all carArray;

... but there's no such construct in C#. You could use:

else
{
    using (var iterator in GetEnumerator())
    {
        while (iterator.MoveNext())
        {
            yield return iterator.Current;
        }
    }
}

or skip GetEnumerator:

else
{
    foreach (var var in carArray)
    {
        yield return car;
    }
}

... but obviously that's pretty ugly.

What you could do is separate out the code so that you only use an iterator block (the kind of method with yield return statements) if you need custom ordering:

// Made return type generic, and improved the name
public IEnumerable<Car> GetTheCars(bool reverseOrder)
{
    return reverseOrder ? GetTheCarsReversed() : carArray;
}

private IEnumerable<Car> GetTheCarsReversed()
{
    for (int i = carArray.Length; i != 0; i--)
    {
        yield return carArray[i - 1];
    }
}

That does have a disadvantage in terms of returning the array reference directly if you're not asking for the reversed order... the caller could then cast to Car[] and modify the array. However, that's probably a nuance that don't need to know about just yet.

people

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