title: Implementation of array with negative indices
body: <p>I am making a game with a world that extends infinitely in every direction. This means that you can be at position <code>X:50</code>, <code>Y:50</code> or <code>X:-50</code>, <code>Y:-50</code>. But... I can't really do that with a normal C# List...</p>
  
  <p>All the ideas I've come up with seem to be too complicated/inefficient to work...</p>