Possible to overload null-coalescing operator?

Question

Is it possible to overload the null-coalescing operator for a class in C#?

Say for example I want to return a default value if an instance is null and return the instance if it's not. The code would look like something like this:

   return instance ?? new MyClass("Default");   

But what if I would like to use the null-coalescing operator to also check if the MyClass.MyValue is set?

Answer 1

Good question! It's not listed one way or another in the list of overloadable and non-overloadable operators and nothing's mentioned on the operator's page.

So I tried the following:

public class TestClass {     public static TestClass operator ??(TestClass  test1, TestClass test2)     {         return test1;     } } 

and I get the error "Overloadable binary operator expected". So I'd say the answer is, as of .NET 3.5, a no.

Answer 2

According to the ECMA-334 standard, it is not possible to overload the ?? operator.

Similarly, you cannot overload the following operators:

• =
• &&
• ||
• ?:
• ?.
• checked
• unchecked
• new
• typeof
• as
• is