"is null" vs "== null"

[Lionello Lunesu]

> I'll venture to say that most people will expect that null == null, and at 
> the very least, it seems that many (most?) people on the NG agree.

What about the general case: ptr == ptr (which includes the case where 
ptr==null: null == null)? Should the compiler inhibit the call to opEquals 
in the general case as well?

But settling this issue will not settle case where one of the arguments to 
"==" is null. I saw some opEquals implementation somewhere that started with 
the line "if (o is null) return false;", which seems silly, since if the 
opEquals would have been called the other way around (b == a, instead of a 
== b) then the program would have surely crashed (being a virtual call, 
"this" must be valid to access the virtual function table). Right? "a==b" 
should in any case be identical to "b==a".

I guess the only thing we can agree on is that the compiler should emit an 
error message when it encounters code like "if (whatever == null)" or "if 
(null == whatever)".

L.