C++ class embind, passing object pointer argument

[guillaume...@gmail.com]

Hi,

I try to pass object pointer argument to method of an embind class. The objet pointer argument is not a embind class.
Here a example of code :

#include <emscripten.h>
#include <bind.h>

using namespace emscripten;


  class A {
      public:
          A () {
              a=5;
          }
          void add() {
              a = a+1;
          }
          int get() {
              return a;
          }
      private:
          int a;
  };

  class B {
      public:
          B () {
              b=10;
          }
          void add() {
              b = b+1;
          }
          int get() {
              return b;
          }

          A* getA() {
              return new A;
          }

          void addA(A* a) {
              b+=a->get();
          }
      private:
          int b;
  };


EMSCRIPTEN_BINDINGS(test) {
    class_<B>("B")
          .constructor<>()
          .function("add",&B::add)
          .function("get",&B::get)
          .function("getA",&B::getA, allow_raw_pointers())
          .function("addA",&B::addA, allow_raw_pointers())
          ;
}

My javascript code :

var B = new Module.B;
var A = B.getA();
B.addA(A);

I get the following error : "ReferenceError: getTypeName is not defined"
I suppose it's because the class A is not embind. I work with big class I don't have to manipulate in javascript, I just have a pointer.

Is it possible to use pointer on class which are not embind ? (like cwrap which return an integer for a pointer)

[Jukka Jylänki]

You can register that class without anything exposed on it, which will allow you to pass pointers to it around in a black-box manner.

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[guillaume...@gmail.com]

Thanks, I try it and it work for my simple example.

But in my project, the class has virtual methods (but no pure virtual)... and I have now this error :
incomplete type 'GuidoParser' used in type trait expression
    : public integral_constant<bool, __is_polymorphic(_Tp)> {};

Any idea ?

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[guillaume...@gmail.com]

OK, it's not the virtual function. It's because this class is referenced in an other file just with "class GuidoParser;" and not with the include file definition.

[Chad Austin]

It sounds like embind currently does not support forward-declared classes because some information about the type definition is necessary at bind type: how to copy the value, destroy it, and so on.

It's probably possible to add support for this functionality.  I wonder if there is a way using C++ templates to determine whether a type is declared or declared-and-defined at bind time.

If not, perhaps an API something like...

opaque_handle<C>("C");

... would work.  You wouldn't be able to bind member functions or constructors or destructors or anything, but you could pass C* pointers around as opaque integers.

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Chad Austin

Technical Director, IMVU

http://engineering.imvu.com

http://chadaustin.me