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

[Wolfgang K. <wol...@xm...>]

Markus,

sorry for the late reply. At a first glance I don't see problems with
the patch you sent. Did you try running the demo applications shipped
with XMLVM to make sure that the patch did not break something or did
you only try running your small sample program?

-- Wolfgang


Markus Heberling wrote:
> Hi,
>
> what about this patch:
>
> @@ -183,11 +183,35 @@ int main(int argc, char* argv[])
>      <xsl:text>
>  @implementation </xsl:text>
>      <xsl:value-of select="vm:fixname(@package)"/>
>      <xsl:text>_</xsl:text>
>      <xsl:value-of select="vm:fixname(@name)"/>
> -
> +
> +
> +    <!-- Emit constructor -->
> +    <xsl:text>
> +-(id)init
> +{
> +    if (self = [super init])
> +    {
> +</xsl:text>
> +      <!-- Emit declarations for all non-static object fields -->
> +      <xsl:for-each select="vm:field[not(@isStatic = 'true') and
> vm:isObjectRef(@type)]">
> +          <xsl:text>        </xsl:text>
> +        <xsl:value-of select="vm:fixname(../@package)"/>
> +        <xsl:text>_</xsl:text>
> +        <xsl:value-of select="vm:fixname(../@name)"/>
> +        <xsl:text>_</xsl:text>
> +        <xsl:value-of select="vm:fixname(@name)"/>
> +        <xsl:text>=[NSNull null];
> +</xsl:text>
> +      </xsl:for-each>
> +<xsl:text>    }
> +    return self;
> +}
> +</xsl:text>
> +
>      <!-- Emit destructor -->
>      <xsl:text>;
>
>  - (void) dealloc;
>  {
>
>
> This creates a constructor in the ObjC-class and fills all instance
> variables of any Object-type with [NSNull null].
>
> This seems to work in my tests, but I don't know if it might break
> anything.
>
> Markus
>
> Am 30.10.2009 um 20:18 schrieb Arno Puder:
>
>>
>> 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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