I ran into this today and have no idea why the C# compiler isn't throwing an error.
Int32 x = 1;
if (x == null)
{
Console.WriteLine("What the?");
}
I'm confused as to how x could ever possibly be null. Especially since this assignment definitely throws a compiler error:
Int32 x = null;
Is it possible that x could become null, did Microsoft just decide to not put this check into the compiler, or was it missed completely?
Update: After messing with the code to write this article, suddenly the compiler came up with a warning that the expression would never be true. Now I'm really lost. I put the object into a class and now the warning has gone away but left with the question, can a value type end up being null.
public class Test
{
public DateTime ADate = DateTime.Now;
public Test ()
{
Test test = new Test();
if (test.ADate == null)
{
Console.WriteLine("What the?");
}
}
}
Best Answer
This is legal because operator overload resolution has a unique best operator to choose. There is an == operator that takes two nullable ints. The int local is convertible to a nullable int. The null literal is convertible to a nullable int. Therefore this is a legal usage of the == operator, and will always result in false.
Similarly, we also allow you to say "if (x == 12.6)", which will also always be false. The int local is convertible to a double, the literal is convertible to a double, and obviously they will never be equal.