Re: [xmlvm-users] Transition of Cross Compatible to Posix

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

Troy,

first of all, the reason for doing the C backend is to fully support the 
Java object model. With the Objective-C backend, this simple Java 
program cannot be cross-compiled:

class Base { int x; }
class Derived extends Base { int x; }

This is just one of several problems when trying to use the Objective-C 
object model to represent Java's object model. The C backend also 
features a fully-fledged garbage collector which was impossible for 
various reasons with Objective-C.

Now to your question: lets assume you have interface I:

interface I {
   public void foo();
}

Then write a Java class as follows:

class I_impl implements I {
   public native void foo();
}

Cross-compile I_impl with the C backend and provide the implementation 
of I_impl.foo() as a C function. If you want I_impl to be a wrapper of 
an Objective-C object, you can add a helper field in Java:

class I_impl implements I {
   private Object wrappedObjectiveCObject;
   public native void foo();
}

Field 'wrappedObjectiveCObject' can then be 'abused' in the C code to 
save a reference to an Objective-C object.

I would also suggest you take a look at xmlvm/doc/slides. There are a 
few slides highlighting some more details of the C backend.

Arno


On 5/9/11 11:00 AM, Troy Gaines wrote:
> Hello everyone,
>
> Here's an issue we're having with the new C-backend.  Originally, we
> started using the cross-compatible Objective C library, which has served
> us well.  We used this for cross-compiling part of the application.  The
> rest we wrote by hand, since the interface was scoped to be different
> between the two platforms.  We're now trying to move to the new C
> back-end but the semantics are now different.
>
> An example is how the Java Interface is cross-compiled.  With the
> cross-compatible library, it would generate an Objective C protocol.  On
> our side, we would create an Objective C class implementing the
> protocol.  With the posix target, it generates a C structure.
>
> What is the recommended way of making this transition?  Am I missing
> something?
>
> And thanks for all the hard work with this project!
>
>
>
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