Warnings when building embind example

[Mo Chen]

I'm trying to following the example here:

https://emscripten.org/docs/porting/connecting_cpp_and_javascript/embind.html#deriving-from-c-classes-in-javascript

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

using namespace emscripten;

struct Interface {
    virtual void invoke(const std::string& str) = 0;
};

struct InterfaceWrapper : public wrapper<Interface> {
    EMSCRIPTEN_WRAPPER(InterfaceWrapper);
    void invoke(const std::string& str) {
        return call<void>("invoke", str);
    }
};

EMSCRIPTEN_BINDINGS(interface) {
    class_<Interface>("Interface")
        .function("invoke", &Interface::invoke, pure_virtual())
        .allow_subclass<InterfaceWrapper>("InterfaceWrapper")
        ;
}

and em++ is giving me this warning:

moche01@gunbuster:~/sandbox/emscripten-play$ em++ -Wall --bind interface.cpp

In file included from interface.cpp:2:
/Users/moche01/sandbox/emscripten-play/emsdk/fastcomp/emscripten/system/include/emscripten/bind.h:459:13: warning: delete called on 'Interface' that is abstract but has non-virtual destructor [-Wdelete-non-virtual-dtor]
            delete ptr;
            ^
/Users/moche01/sandbox/emscripten-play/emsdk/fastcomp/emscripten/system/include/emscripten/bind.h:1276:32: note: in instantiation of function template specialization 'emscripten::internal::raw_destructor<Interface>'
      requested here
            auto destructor = &raw_destructor<ClassType>;
                               ^
interface.cpp:18:5: note: in instantiation of member function 'emscripten::class_<Interface, emscripten::internal::NoBaseClass>::class_' requested here
    class_<Interface>("Interface")
    ^
In file included from interface.cpp:2:
/Users/moche01/sandbox/emscripten-play/emsdk/fastcomp/emscripten/system/include/emscripten/bind.h:459:13: warning: delete called on non-final 'InterfaceWrapper' that has virtual functions but non-virtual destructor
      [-Wdelete-non-virtual-dtor]
            delete ptr;
            ^
/Users/moche01/sandbox/emscripten-play/emsdk/fastcomp/emscripten/system/include/emscripten/bind.h:1276:32: note: in instantiation of function template specialization 'emscripten::internal::raw_destructor<InterfaceWrapper>'
      requested here
            auto destructor = &raw_destructor<ClassType>;
                               ^
/Users/moche01/sandbox/emscripten-play/emsdk/fastcomp/emscripten/system/include/emscripten/bind.h:1373:24: note: in instantiation of member function 'emscripten::class_<InterfaceWrapper, emscripten::base<Interface>
      >::class_' requested here
            auto cls = class_<WrapperType, base<ClassType>>(wrapperClassName)
                       ^
interface.cpp:20:10: note: in instantiation of function template specialization 'emscripten::class_<Interface, emscripten::internal::NoBaseClass>::allow_subclass<InterfaceWrapper>' requested here
        .allow_subclass<InterfaceWrapper>("InterfaceWrapper")
         ^
2 warnings generated.

I understand this is saying that Interface doesn't have a virtual destructor.  My question is: why is embind trying to call 'delete' on the interface?  In the case where I don't have control over the source code of the Interface class, can I wrap the interface in a way that doesn't produce this warning?

Thanks,

Mo

[Shachar Langbeheim]

Hi,
this isn't an embind issue - c++ compiler requires that abstract classes implement a virtual destructor.
https://stackoverflow.com/questions/8764353/what-does-has-virtual-method-but-non-virtual-destructor-warning-mean-durin

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