C# multidimensional immutable array

There isn't the equivalent of a rectangular array as far as I'm aware, but you could:

• Have an ImmutableList<ImmutableList<Point>>
• Wrap a single ImmutableList<Point> in your own class to provide access across two dimensions.

The latter would be something like:

// TODO: Implement interfaces if you want
public class ImmutableRectangularList<T>
{
    private readonly int Width { get; }
    private readonly int Height { get; }
    private readonly IImmutableList<T> list;

    public ImmutableRectangularList(IImmutableList<T> list, int width, int height)
    {
        // TODO: Validation of list != null, height >= 0, width >= 0
        if (list.Count != width * height)
        {
            throw new ArgumentException("...");
        }
        Width = width;
        Height = height;
        this.list = list;
    }

    public T this[int x, int y]
    {
        get
        {
            if (x < 0 || x >= width)
            {
                throw new ArgumentOutOfRangeException(...);
            }
            if (y < 0 || y >= height)
            {
                throw new ArgumentOutOfRangeException(...);
            }
            return list[y * width + x];
        }
    }
}