How can a list with one member be useful?

Question

I read an SO which asked for the easiest way to create a list with a one member.

Quick way to turn object into single-element list?

This raised a question for me, when would this be useful?

I can't think of an example when I would use a List<T> with a single member over just the T variable itself.

Can someone explain or provide an example?

Answer 1

In general, this happens when you have a logical collection of elements that just happens to contain one member. For example, you might have a House class with a collection of Room items, but the OneRoomSchoolhouse class only has one object in its Rooms collection.

As another example, you might have a method with this signature:

void LogNewItems(List<Item> newItems);

If you have only one item, you would have to pass it thus:

LogNewItems(new List<Item> { item });

In fact, if you're designing the item-logging API, you might create a convenience method so developers don't have to do that. The method could look something like this:

void LogNewItem(Item item)
{
    LogNewItems(new List<Item> { item });
}