Can a SortedList be accessed with a negative index?

[Jen]

I'm looking at some old C# code and I found a line where a SortedList is
being accessed with a negative index, like so:

groups[-1];

My C# skills must be getting rusty. How can that work? What does it do?

 

[Jeroen Mostert]

I'm looking at some old C# code and I found a line where a SortedList is
being accessed with a negative index, like so:

groups[-1];

My C# skills must be getting rusty. How can that work? What does it do?

A SortedList is actually a dictionary -- the name is particularly poorly
chosen because the class is not very suitable for an *actual* sorted list
either.

The keys of a SortedList can be arbitrary objects; in this case, integers.
Those don't have to be nonnegative (or consecutive).

What you're thinking of is that the items can *also* be accessed by ordinal
[0..Count), but that's through the .GetByIndex() method.