Why does the is keyword require a non-null expression?

Question

The MSDN documentation for the is keyword says:

expression is not null

Why? If MethodThatReturnsNull() is type were called shouldn't that return false since null certainly isn't that type?

score 5 · Accepted Answer · answered Jun 12 '09 at 21:14

5

It does return false if expression is null. Perhaps you're misunderstanding the documentation?

answered Jun 12 '09 at 21:14

mqp

Correct. MSDN states "An is expression evaluates to true if the provided expression is non-null, and the provided object can be cast to the provided type without causing an exception to be thrown." So it is false if expression is null. – Dirk Vollmar Jun 12 '09 at 21:44
I've voted to close it since it's not really relevant anymore, considering my mistake. – jasonh Jun 12 '09 at 21:45

score 0 · Answer 2 · answered Jun 12 '09 at 21:13

0

The only thing you can say for certain about null is that you don't know what it is. Comparing something to null generally has a result of null ...

Q: Does 1 == "I don't know"? A: "I dont know"

Check out this blog post by Eric Lippert.

answered Jun 12 '09 at 21:13

JP Alioto

score 0 · Answer 3 · answered Jun 12 '09 at 21:14

0

You can't statically resolve a null.

answered Jun 12 '09 at 21:14

Jason Watts

score 0 · Answer 4 · edited May 23 '17 at 12:01

0

This was a pretty popular answer I gave to a similar question.

That's like asking what kind of cake would have been in an empty box with no label.

edited May 23 '17 at 12:01

Community

answered Jun 12 '09 at 21:15

Josh

According to the C# compiler and .NET framework, it's not a type cake. :) – jasonh Jun 13 '09 at 01:33

4 Answers4