Re: [xmlvm-users] Default values of member variables

[Arno P. <ar...@pu...>]

this is a tricky issue. Objective-C initializes member variables to 
'nil' by default (which, I believe, is represented by 0x0). However, in 
XMLVM we cannot map Java's null to Objective-C's nil, because nil is not 
accepted as an argument to some data structures (e.g., NSArray, 
NSDictionary, etc). That is why we map null to [NSNull null].

Now, very unfortunate, you cannot do something like this in Objective-C:

@interface Foo {
id ref = [NSNull null];
}
@end

This means, you have do some fancy code generation. This is a known 
issue in XMLVM. In the meantime, you can explicitly initialize Java 
members such as:

public class Test {
   Object ref = null;
...

Arno


Panayotis Katsaloulis wrote:
> On 30 Οκτ 2009, at 8:35 μ.μ., Markus Heberling wrote:
> 
>> Hi,
>>
>> take this code convert it to objc and run it:
>>
>> public class Test{
>>   Object thisIsNotInitialized;
>>
>>   void test(){
>>        if(thisIsNotInitialized==null)
>>            System.out.println("null");
>>   }
>>
>>   public static void main(String[] args){
>>       new Test().test();
>>   }
>> }
>>
>> I would expect to get "null" printed to the console. But that  
>> doesn't happen. The generated if is something like thos:
>>
>> if (_op1.o != [NSNull null]) goto label0;
>>
>> So it checks for [NSNull null]. But _op1.o contains 0x0 and the  
>> check is false. So I would guess that the initialization code of the  
>> ObjC variables has to be changed so that they contain [NSNull null]  
>> and not 0x0 by default.
>>
>> Hope you get what I mean.
> 
> 
> 
> If a selector returns nil, what is seen in Java?
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