Emulating boost::python::extract

[eudoxos]

I am using the following helper struct to emulate boost::python::extract<T> in legacy code. For those who don't remember, it tried to extract c++ object from whatever was given to it, using the whole conversion machinery.

Can someone have a look whether the code is doing anything obviously wrong, especially regarding reference counting or similar low-level things? I now seeing crashes in this code (somewhere, not in the debug mode, so not sure exactly) and might get some hint from a review.

namespace pybind11{
	template<typename T>
	struct __attribute__((visibility("hidden"))) extract{
		const object& obj;
		extract(const object& obj_): obj(obj_){}
		bool check(){ try{ cast<T>(obj); return true; } catch(...){ return false; }  }
		T operator()() const { return cast<T>(obj); }
		operator T() const { return cast<T>(obj); }
	};
};

The usage is something like this:

  py::extract<std::string> exS(obj);
  py::extract<int> exI(obj)
  if(exS.check()) str=exS();
  // ...

Is there maybe some similar device in pybind11, perhaps just wrapping the cast attempt and exception catch logic in a nicer package?