Question

Here’s an example:

static int Main(string[] args)
{
    foreach(string arg in args.Skip(77))
    {
        Console.WriteLine(arg);
    }

    return 0;
}

Assuming enough args, does this call MoveNext 77 times inside Skip? Or does Skip jump straight to the appropriate index?

Answer 1

Embarrassingly, I was wrong.

No.

public static IEnumerable<TSource> Skip<TSource>(this IEnumerable<TSource> source, int count) {
    if (source == null) throw Error.ArgumentNull("source"); 
    return SkipIterator<TSource>(source, count); 
}

static IEnumerable<TSource> SkipIterator<TSource>(IEnumerable<TSource> source, int count) {
    using (IEnumerator<TSource> e = source.GetEnumerator()) {
        while (count > 0 && e.MoveNext()) count--;
        if (count <= 0) { 
            while (e.MoveNext()) yield return e.Current;
        } 
    } 
}

Jon Skeet explains why it can’t do that.