Question

I have a query about type of null.
I have a small program can anyone tell me about this.

public class TestApplication
{
    public void ShowText(object  ob)
    {
        Console.Write("Inside object");
    }
    public void ShowText(string str)
    {
        Console.Write("Inside string");
    }
    public void ShowText(int i)
    {
        Console.Write("Inside int.");
    }
    public void ShowText(char c)
    {
        Console.Write("Inside Character");
    }
    static void Main(string[] args)
    {
        new TestApplication().ShowText(null);            
        Console.Read();
    }
}

Why it call the string function.
Is it means the type of null is string.
It might look a foolish conclusion but I am not able to find the region why it is calling the function of string.

Answer 1

Your question about the type of the null literal is answered here: What is the type of null literal?

But that doesn’t really matter when talking about overload resolution. The actual null value itself will automatically be converted to whatever type it ends up as.

As for why the string overload is called:

1. You can’t pass null as int and char parameters as they’re value types, so those two overloads are out. (They could have been candidates had you made them nullable int? and char? types, but I won’t go into that.)

2. Between the two other overloads taking reference types, string is a more specific type than object. That is, it derives from (and is therefore implicitly convertible to) object. Further, from the following section in the C# language spec (emphasis mine):

   7.5.3.5 Better conversion target

   Given two different types T1 and T2, T1 is a better conversion target than T2 if at least one of the following holds:

   • An implicit conversion from T1 to T2 exists, and no implicit conversion from T2 to T1 exists

   • …

Thus, the string overload is chosen as the best fit.