Extension method for IEnumerable

gistfile1.cs

public static class IEnumerableExtensions {
	public static IEnumerable<TSource> Alternate<TSource>(this IEnumerable<TSource> self, IEnumerable<TSource> with) {
		using (var selfEnumerator = self.GetEnumerator())
		using (var withEnumerator = with.GetEnumerator()) {

			bool selfHasCurrent;
			bool withHasCurrent;

			do {
				selfHasCurrent = selfEnumerator.MoveNext();
				withHasCurrent = withEnumerator.MoveNext();

				if (selfHasCurrent) yield return selfEnumerator.Current;
				if (withHasCurrent) yield return withEnumerator.Current;

			} while (selfHasCurrent || withHasCurrent);
		}
	}
	
	public static T FirstOrNew<T>(this IEnumerable<T> list, Func<T, bool> predicate) where T : class, new() {
		return list.FirstOrDefault(predicate) ?? new T();
	}
}