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

[Markus H. <ma...@ti...>]

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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