Interesting use of the C# yield keyword in Nerd Dinner tutorial

Question

Working through a tutorial (Professional ASP.NET MVC - Nerd Dinner), I came across this snippet of code:

public IEnumerable GetRuleViolation         


        

Answer 1

1) Take this simpler example:

public void Enumerate()
{
    foreach (var item in EnumerateItems())
    {
        Console.WriteLine(item);
    }
}

public IEnumerable EnumerateItems()
{
    yield return "item1";
    yield return "item2";
    yield break;
}

Each time you call MoveNext() from the IEnumerator the code returns from the yield point and moves to the next executable line of code.

2) yield break; will tell the IEnumerator that there is nothing more to enumerate.

3) once per enumeration.

Using yield break;

public IEnumerable EnumerateUntilEmpty()
{
    foreach (var name in nameList)
    {
        if (String.IsNullOrEmpty(name)) yield break;
        yield return name;
    }     
}