Other ways to deal with “loop initialization” in C#

Question

To start with I\'ll say that I agree that goto statements are largely made irrelevant by higher level constructs in modern programming languages and shouldn\'t be used when

Answer 1

Personally I like Mark Byer's option, but you could always write your own generic method for this:

public static void IterateWithSpecialFirst(this IEnumerable source,
    Action firstAction,
    Action subsequentActions)
{
    using (IEnumerator iterator = source.GetEnumerator())
    {
        if (iterator.MoveNext())
        {
            firstAction(iterator.Current);
        }
        while (iterator.MoveNext())
        {
            subsequentActions(iterator.Current);
        }
    }
}

That's relatively straightforward... giving a special last action is slightly harder:

public static void IterateWithSpecialLast(this IEnumerable source,
    Action allButLastAction,
    Action lastAction)
{
    using (IEnumerator iterator = source.GetEnumerator())
    {
        if (!iterator.MoveNext())
        {
            return;
        }            
        T previous = iterator.Current;
        while (iterator.MoveNext())
        {
            allButLastAction(previous);
            previous = iterator.Current;
        }
        lastAction(previous);
    }
}

EDIT: As your comment was concerned with the performance of this, I'll reiterate my comment in this answer: while this general problem is reasonably common, it's not common for it to be such a performance bottleneck that it's worth micro-optimizing around. Indeed, I can't remember ever coming across a situation where the looping machinery became a bottleneck. I'm sure it happens, but that isn't "common". If I ever run into it, I'll special-case that particular code, and the best solution will depend on exactly what the code needs to do.

In general, however, I value readability and reusability much more than micro-optimization.