Re: SWIGUpcast problem / assigning to .. from incompatible type

I've put up a question in StackOverflow about this issue where I elaborated
the problem a bit more:

https://stackoverflow.com/questions/63174786/how-to-wrap-handles-to-class-hierarchy-in-swig-for-java

and there is also a self contained ready to run demo on github:

https://github.com/nyholku/swig-experiments

wbr Kusti



> On 29 Jul 2020, at 12.05, Kustaa Nyholm <[email protected]> wrote:
> 
> Hi,
> 
> I've been posting a few post about this problem already so sorry about the noise.
> 
> But I think I've tracked the root cause.
> 
> Background: I'm trying to upgrade existing occjava from OCE to OCC 7.3.0.
> 
> The main problem I'm experiencing stems from the fact that OCC 7.0.0
> gave gave up a hierarchy of classes Handle_XXX and replaced that with
> opencascade::handle<XXX> (hidden behind macro DEFINE_STANDARD_HANDLE).
> 
> In the OCC context Handle is basically a pointer to a pointer to the
> actual instance of a class and originally the Handle_XXXX hierarchy
> mirrored the actual class hierarchy.
> 
> And this made the upcasting work with the occjava SWIG defs.
> 
> But now it fails cause every Handle_XXX (aka opencascade::handle<XXX>)
> is a distinct type.
> 
> So I'm looking for ideas how to fix this. Preferably with a typemap
> or few cause there are a lot of classes and handles in OCC (over
> 8000 files in /usr/local/include/opencascade).
> 
> I've made a minimal (if not totally self contained experiment project
> to illustrate the problem).
> 
> You can download a zip file of the experiment here:
> 
> http://eazycnc.com/temp/experiments.zip
> 
> and I will also collect the gist of it below.
> 
> wbr Kusti
> 
> 
> /// Standard_Handle.hxx (FRAGMENT) ---------------------------
> template <class T>
>  class handle
>  {
>  public:
>    //! STL-compliant typedef of contained type
>    typedef T element_type;
>    ...
>   handle () : entity(0) {}
> 
>    //! Constructor from pointer to new object
>    handle (const T *thePtr) : entity(const_cast<T*>(thePtr))
>    {
>      ...
>    }
> ...
>  private:
>    Standard_Transient* entity;
>  };
> ...
> #define DEFINE_STANDARD_HANDLECLASS(C1,C2,BC) class C1; typedef Handle(C1) Handle_##C1;
> #define DEFINE_STANDARD_HANDLE(C1,C2) DEFINE_STANDARD_HANDLECLASS(C1,C2,Standard_Transient)
> #define DEFINE_STANDARD_PHANDLE(C1,C2) DEFINE_STANDARD_HANDLECLASS(C1,C2,Standard_Persistent)
> 
> 
> /// experiment.hxx --------------------------------------------
> #include "/usr/local/include/opencascade/Standard_Handle.hxx"
> 
> DEFINE_STANDARD_HANDLE(Geom_Geometry,Standard_Transient);
> DEFINE_STANDARD_HANDLE(Geom_Curve,Standard_Transient);
> 
> 
> /// experiment.cxx --------------------------------------------
> #include "experiment.hxx"
> 
> 
> /// experiment.i ----------------------------------------------
> %module experiment
> %{
> #include "experiment.hxx"
> %}
> 
> %include "experiment.hxx"
> 
> %rename(Geom_Curve) Handle_Geom_Curve;
> %rename(Geom_Geometry) Handle_Geom_Geometry;
> 
> class Handle_Geom_Geometry
> {
> 	Handle_Geom_Geometry()=0;
> };
> 
> class Handle_Geom_Curve : public Handle_Geom_Geometry
> {
> 	Handle_Geom_Curve()=0;
> };
> 
> 
> /// Makefile ---------------------------------------------------
> all:
> 	c++ -std=c++11 -c -I/usr/local/include/opencascade -o experiment.so experiment.cxx
> 	swig -c++ -java experiment.i
> 	c++ -std=c++11 -c -I/usr/local/include/opencascade -I/Library/Java/JavaVirtualMachines/jdk-11.0.6.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/jdk-11.0.6.jdk/Contents/Home/include/darwin -o experiment_wrap.so experiment_wrap.cxx
> 
> 
> /// experiment_wrap.cxx (FRAGMENT) -----------------------------
> 
> SWIGEXPORT jlong JNICALL Java_experimentJNI_Geom_1Curve_1SWIGUpcast(JNIEnv *jenv, jclass jcls, jlong jarg1) {
>    jlong baseptr = 0;
>    (void)jenv;
>    (void)jcls;
>    *(Handle_Geom_Geometry **)&baseptr = *(Handle_Geom_Curve **)&jarg1;
>    return baseptr;
> }
> 
> 
> which fails to compile like this
> 
> 
> 
> // Error ========================================================
> 
> experiment_wrap.cxx:266:42: error: assigning to 'Handle_Geom_Geometry *' (aka 'handle<Geom_Geometry> *') from incompatible type 'Handle_Geom_Curve *' (aka 'handle<Geom_Curve> *')
>    *(Handle_Geom_Geometry **)&baseptr = *(Handle_Geom_Curve **)&jarg1;
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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