How to remove elements from a generic list while iterating over it?

Question

I am looking for a better pattern for working with a list of elements which each need processed and then depending on the outcome are removed from

Answer 1

Copy the list you are iterating. Then remove from the copy and interate the original. Going backwards is confusing and doesn't work well when looping in parallel.

var ids = new List { 1, 2, 3, 4 };
var iterableIds = ids.ToList();

Parallel.ForEach(iterableIds, id =>
{
    ids.Remove(id);
});