Re: [Swig-user] Bug with nested templates (wrapping C++ in Java with Swig 3.0)

[William S F. <ws...@fu...>]

On 6 August 2015 at 19:35, Sven Wegener <sve...@gm...> wrote:
> Hello,
> I need your help with wrapping the following short, self-contained example
> to Java.
>
> The code below declares two template classes, Mixin1 and Mixin2. Then
> another class, "Product", is declared, which again is templated to depend
> on either Mixin1 or Mixin2.
>
> The problem is, that I have to give some generic name ("AnyMixin" below) to
> the Product template argument, and that swig uses this generic name in
> the wrapper
> rather than the actual name (Mixin1 or Mixin2) which instantiates the
> template.
>
> Swig produces the following code:
> --- Mixins_wrap.cxx ---
> [...]
> SWIGEXPORT void JNICALL Java_testJNI_intMixin1Product_1m_1set(JNIEnv *jenv,
> jclass jcls, jlong jarg1, jobject jarg1_, jlong jarg2) {
>   Product< int,Mixin1 > *arg1 = (Product< int,Mixin1 > *) 0 ;
>   AnyMixin< int > arg2 ;
>   AnyMixin< int > *argp2 ;
> [...]
> ------------------------
>
> and the compiler doesn't know about AnyMixin, of course:
> --- compiler output: ---
> Mixins_wrap.cxx:226:3: error: ‘AnyMixin’ was not declared in this scope
>    AnyMixin< int > arg2 ;
> [...]
> ------------------------
>
> Do you have any suggestion, how to wrap the example below without messing
> around with the code itself? The full code has 25 Mixins and 12 Product
> classes, so that I *need* the template mechanism, if I don't want to write
> 300 classes by hand.
>
> To reproduce the problem, simply save the code below as "Mixins.H" and
> execute:
>
>   export CPPFLAGS= -I$(JAVA_HOME)/include -I$(JAVA_HOME)/include/linux
>   swig3.0 -java -c++ Mixins.H
>   g++ -c $(CPPFLAGS)  Mixins_wrap.cxx
>
> --- Mixins.H ---
> #ifdef SWIG
> %module test
> %{
> #include  "Mixins.H"
> template <class T> Mixin1<T>::Mixin1(T x){ this->x=x; }
> template <class T> Mixin2<T>::Mixin2(T x){ this->x=x; }
> template <class T,template<class> class AnyMixin>
> Product<T,AnyMixin>::Product(AnyMixin<T> m){ this->m=m; }
> %}
>
> #endif
>
> template <class T> class Mixin1{
> public:
>   T x;
>   Mixin1(T x=0);
> };
> template <class T> class Mixin2{
> public:
>   T x;
>   Mixin2(T x=0);
> };
>
> template <class T, template<class> class AnyMixin> class Product{
> public:
>   AnyMixin<T> m;
>   Product(AnyMixin<T>);
> };
>
> #ifdef SWIG
>   %template(intMixin1Product) Product<int,Mixin1 >;
>   %template(intMixin2Product) Product<int,Mixin2 >;
> #endif
> -----------------

I'm afraid that template template parameters are poorly supported and
development in SWIG is required to make this work. Sorry, someone
needs to do this.

Regards
William