Why does the code get compiled when I use !!= C#

June 27, 2022

I am trying to understand how does the code get compiled when I use (!!=)
Apparently the 2 snippets below do the same thing.
Why are both permissable?

if (4 !!= 5)
  Console.WriteLine("vvvvvv");

the above does the same thing as:

if (4 != 5)
   Console.WriteLine("vvvvvv");

>Solution :

The expression 4 !!= 5 is parsed as the null-forgiving operator applied to 4, and then != applied to that expression and 5. That is, (4!) != 5.

According to the draft spec, a null forgiving expression is a kind of primary expression:

primary_expression
    : ...
    | null_forgiving_expression
    ;

null_forgiving_expression
    : primary_expression '!'
    ;

and that:

The postfix ! operator has no runtime effect – it evaluates to the result of the underlying expression. Its only role is to change the null state of the expression to "not null", and to limit warnings given on its use.

In other words, the ! after 4 does nothing and is very redundant. The constant 4 is never null after all 🙂