Generic List - moving an item within the list

var item = list[oldIndex];

list.RemoveAt(oldIndex);

if (newIndex > oldIndex) newIndex--; 
// the actual index could have shifted due to the removal

list.Insert(newIndex, item);

Put into Extension methods they look like:

    public static void Move<T>(this List<T> list, int oldIndex, int newIndex)
    {
        var item = list[oldIndex];

        list.RemoveAt(oldIndex);

        if (newIndex > oldIndex) newIndex--;
        // the actual index could have shifted due to the removal

        list.Insert(newIndex, item);
    }

    public static void Move<T>(this List<T> list, T item, int newIndex)
    {
        if (item != null)
        {
            var oldIndex = list.IndexOf(item);
            if (oldIndex > -1)
            {
                list.RemoveAt(oldIndex);

                if (newIndex > oldIndex) newIndex--;
                // the actual index could have shifted due to the removal

                list.Insert(newIndex, item);
            }
        }

    }

List<T>.Remove() and List<T>.RemoveAt() do not return the item that is being removed.

Therefore you have to use this:

var item = list[oldIndex];
list.RemoveAt(oldIndex);
list.Insert(newIndex, item);

Insert the item currently at oldIndex to be at newIndex and then remove the original instance.

list.Insert(newIndex, list[oldIndex]);
if (newIndex <= oldIndex) ++oldIndex;
list.RemoveAt(oldIndex);

You have to take into account that the index of the item you want to remove may change due to the insertion.

I would expect either:

// Makes sure item is at newIndex after the operation
T item = list[oldIndex];
list.RemoveAt(oldIndex);
list.Insert(newIndex, item);

... or:

// Makes sure relative ordering of newIndex is preserved after the operation, 
// meaning that the item may actually be inserted at newIndex - 1 
T item = list[oldIndex];
list.RemoveAt(oldIndex);
newIndex = (newIndex > oldIndex ? newIndex - 1, newIndex)
list.Insert(newIndex, item);

... would do the trick, but I don't have VS on this machine to check.

Simplest way:

list[newIndex] = list[oldIndex];
list.RemoveAt(oldIndex);

EDIT

The question isn't very clear ... Since we don't care where the list[newIndex] item goes I think the simplest way of doing this is as follows (with or without an extension method):

    public static void Move<T>(this List<T> list, int oldIndex, int newIndex)
    {
        T aux = list[newIndex];
        list[newIndex] = list[oldIndex];
        list[oldIndex] = aux;
    }

This solution is the fastest because it doesn't involve list insertions/removals.