Binding a closure to a std::function to call it from C++... safe to do ?

[krakengore]

Thanks! yeah i did exactly that and noticed the closure function pointer in C 
is written as `returnType (*)(Args... args, void* env)` with additional 
parameters prepended before the env pointer.

Is there a way to attach a nim destructor to an imported cpp object that will 
both call the C++ destructor and GC_unref the closure ?