Extend "object" with a null check more readable than ReferenceEquals

Question

I tried to extend "object" to allow a more readable check if an object is null.

Now, object.ReferenceEquals really checks for a null object, (the rare times it will not apply are since the operator == can be overridden. the object.Equals(null) method can also be overridden).

But the object.ReferenceEquals(null, obj); is not too readable is it?... So, I thought, why not write an extension method to the System.object that will provide that check using object.IsNull(obj);

I've tried:

public static class MyExtClass
{
    // the "IsNull" extension to "object"  
    public static bool IsNull(this object obj)
    {
        return object.ReferenceEquals(obj, null);
    }
}

public SomeOtherClass
{
     public static void TryUsingTheExtension()
     {
          object obj;

          // Why does this line fail? the extension method is not recognized
          // I get: 'object' does not contain a definition for "IsNull"
          bool itIsANull = object.IsNull(obj);
     }
}

What did I miss?

Answer 1

Extension methods can be invoked only on instance and not on a class that they extend. So this line of code bool itIsANull = object.IsNull(obj); is incorrect because object is type and not an instance. Change it to :

bool itIsANull = (new object()).IsNull();

Or you can call it on class MyExtClass but not on object class (which is located in mscore.lib) :

MyExtClass.IsNull(new object());

P.S. It looks like you missed something about extension methods. The truth is that they have nothing to do with classes that they extend. It's just a convenience that is provided for us by Intellisense with use of reflection.

Object class is located in mscorelib and is immutable. You can't add something to it. But what really happens is that Intellisense searches for all public methods that are located in public static classes and accept first argument with keyword 'this' as parameter. If one is found it's 'mapped' to the class that it extends. So when we type obj.MyExtMethod() on instance of that class it is automatically converted by compiler to Helper.MyExtMethod(obj); (if helper is our static class);