How can I quickly up-cast object[,] into double[,]?

Solution 1:

object[,] src = new object[2, 3];

// Initialize src with test doubles.
src[0, 0] = 1.0;
src[0, 1] = 2.0;
src[0, 2] = 3.0;
src[1, 0] = 4.0;
src[1, 1] = 5.0;
src[1, 2] = 6.0;

double[,] dst = new double[src.GetLength(0), src.GetLength(1)];
Array.Copy(src, dst, src.Length);

Solution 2:

I wouldn't say that there is one way that's faster than another so long as you don't do anything stupid. I'd say that, if you can, cast them when you access them rather than up front. Of course this depends on how you intend to access them. If you're going to index into the array more than once then the cost of unboxing might start to get too much. If you're only scanning the array once, then cast as you go.