If I had to guess (and I should really just look at the code), the "==" and "!=" operators when applied to strings in ChucK end up doing a string comparison, NOT a pointer comparison or reference comparison. In most cases this is what people would want, because they want to be able to write things like this: if(x == "hi there") doThatThing(); if(y != "you suck") doTheOtherThing(); This method/function will interrogate the left- and right-hand objects to determine whether or not the strings are the same. In the case you gave, Robert, the right-hand object is null, which is why you get the null pointer exception. Hans, the bus error that you're seeing is a result of the fact that you are trying to print out a null value. Your code isn't even getting to the conditional. andy On Wed, Jun 24, 2009 at 12:30 PM, Hans Aberg wrote:

On 24 Jun 2009, at 21:12, Robert Poor wrote:

...

I'm so baffled that this must be easy.  What is the proper test to see if a string is null?  More to the point, why does the following code bomb out on the conditional test?

"foo.txt" => string g; <<< g >>>;                      // prints '"foo.txt" : (string)' if (g != null) {                        // evidently crashes here with "[chuck](VM) NullPointerException (during string op)..."  <<< "not null" >>>; } else {  <<< "is null" >>>; }

Possibly you have discovered a new type in ChucK :-):

One would expect there to be two types: copy-over data types and reference types. And null tests should only be applicable to the latter, as the former do not have explicit references. So if strings were reference types, you should have an @=> there, and get an error on =>. If I change your example to: null => string g; <<< g >>>;                      // prints '"foo.txt" : (string)' if (g != null) {                        // evidently crashes here with "[chuck](VM) NullPointerException (during string op)..."  <<< "not null" >>>; } else {  <<< "is null" >>>; }

Then 'chuck' hangs for a while, and then (it or the system) reports "bus error".

 Hans

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