Why does .NET 4.0 sort this array differently than .NET 3.5?

Question

This stackoverflow question raised an interesting question about sorting double arrays with NaN values. The OP posted the following code:

static void Main(st         


        

Answer 1

It's a bug fix. The feedback report with the bug details is here. Microsoft's response to the bug report:

Note that this bug affects the following:

• Array.Sort(), where the array contains Double.NaN
• Array.Sort(), where the array contains Single.NaN
• any callers of above, for example on List.Sort(), where list contains Double.NaN

This bug will be fixed in the next major version of the runtime; until then you can work around this by using a custom IComparer that does the correct sorting. As mentioned in the workaround comments, don't use Comparer.Default, because this is special-cased with a shortcut sort routine that doesn't handle NaN correctly. Instead, you can provide your own comparer that provides an equivalent comparision, but won't be special-cased.