Question

I don’t understand how Current can be null and the LINQ function Last() can return an object. I thought Last uses GetEnumerator and keeps going until current == null and returns the object. However as you can see the first GetEnumerator().Current is null and last somehow returns an object.

How does linq Last() work?

items.GetEnumerator().Current
items.Last()

Answer 1

From using Reflector on System.Core.dll:

public static TSource Last<TSource>(this IEnumerable<TSource> source)
{
    if (source == null)
    {
        throw Error.ArgumentNull("source");
    }
    IList<TSource> list = source as IList<TSource>;
    if (list != null)
    {
        int count = list.Count;
        if (count > 0)
        {
            return list[count - 1];
        }
    }
    else
    {
        using (IEnumerator<TSource> enumerator = source.GetEnumerator())
        {
            if (enumerator.MoveNext())
            {
                TSource current;
                do
                {
                    current = enumerator.Current;
                }
                while (enumerator.MoveNext());
                return current;
            }
        }
    }
    throw Error.NoElements();
}