How to test for NaN with generics (or why NaN.Equals(NaN) == true)?
c#, iequatable
Solution
but Equals is returning true for double.NaN
Yes. And it does regardless of generics:
double x = double.NaN;
Console.WriteLine(x.Equals(x)); // True
Console.WriteLine(x == x); // False
Note that if the second line printed False, that would either make the `IEquatable<T>.Equals` inconsistent with the `Equals(object)` override, or you'd have to make `Equals(object)` violate the reflexivity requirement of `object.Equals(object)`.
Basically this sort of thing is nasty whatever you do with it.
Given that you're trying to find max/min values, you might want to try using `IComparable<T>` instead of `IEquatable<T>` - that may well let you detect NaN in other ways. (I don't have time to check right now.)
Problem
I need to find min and max values in an array (not taking into for possible NaN values in this array). This would be easy only working with `double`, but these FindMin and FindMax functions have to work with generics types. I have tried to test for generic NaNs in this way: ``` bool isNaN<T>(T value) where T : IEquatable<T> { return !value.Equals(value); } ``` but `Equals` is returning `true` for `double.NaN` ??!! I have a workaround like this for now: ``` bool isNaN<T>(T value) where T : IEquatable<T> { var d = value as double?; if (d.HasValue) { return double.IsNaN(d.Value); } return !value.Equals(value); } ``` My question is more about understanding why first solution did not work, is this a bug ? You can find small test code here