Cache()

public static IEnumerable<T> Cache<T>(this IEnumerable<T> source)
{
    return CacheHelper(source.GetEnumerator());
}

private static IEnumerable<T> CacheHelper<T>(IEnumerator<T> source)
{
    var isEmpty = new Lazy<bool>(() => !source.MoveNext());
    var head = new Lazy<T>(() => source.Current);
    var tail = new Lazy<IEnumerable<T>>(() => CacheHelper(source));

    return CacheHelper(isEmpty, head, tail);
}

private static IEnumerable<T> CacheHelper<T>(
    Lazy<bool> isEmpty, 
    Lazy<T> head, 
    Lazy<IEnumerable<T>> tail)
{
    if (isEmpty.Value)
        yield break;

    yield return head.Value;
    foreach (var value in tail.Value)
        yield return value;
}

var cached = mySequence.Cache();