public static class ListExtensions
{
    public static void ForEach<T1, A1>(this List<T1> list, Func<T1, A1, bool> @if, Action<T1, A1> then, A1 arg1)
    {
        for (int i = 0; list != null && i < list.Count; ++i)
        {
            if (@if(list[i], arg1))
            {
                then(list[i], arg1);
            }
        }
    }
}