CS8625 Cannot convert null literal to non-nullable reference type warning for Interlocked.Exchange(ref c, null)

Question

The following code works properly in .NET core 3.1, but generates wrongly the warning CS8625 Cannot convert null literal to non-nullable reference type :

#nullable enable
using System.Threading;

namespace InterlockedExchangeNullProblem {
  public class Class1 {
    public Class1() {
      object? o = new object();
      var o1 = Interlocked.Exchange(ref o, null); // ok
      class2? c = new class2();
      var c1 = Interlocked.Exchange(ref c, null); // error CS8625 Cannot convert null literal to non-nullable reference type.
    }
  }
  public class class2{}
}

If it works for object? , it should also work for class2? .

Answer 1

Solution:

var c2 = Interlocked.Exchange<class2?>(ref c, null);

Note: The compiler made c1 of type class2 instead class2? .

If you agree that this needs to be corrected, then please upvote:

developercommunity.visualstudio.com: Interlocked.Exchange: compiler choses wrong Exchange with nullable types