On 02/06/2012 08:33 PM, Jay Riley wrote:
I'm trying to wrap a C++ class into python. I need to pass an enum value by
reference through a virtual function. I'm doing it like so (non relevant code
omitted):
class BasicRMLScreenWrap : public BasicRMLScreen { public:
bool HandleKeyPressedDefault(const sf::Uint32 time, const ::Input::InputModule* inputModule,
::Input::PlayerInput pinput, ::Input::InputAction& iaction) {
return BasicRMLScreen::HandleKeyPressed(time, inputModule, pinput, iaction);
} bool HandleKeyReleased(const sf::Uint32 time, const ::Input::InputModule*
inputModule, ::Input::PlayerInput pinput, ::Input::InputAction& iaction) override
{ return call_method<bool>(self,
"HandleKeyReleased", time, ptr(inputModule), pinput, boost::ref(iaction));
} private: PyObject* self; };
class_<BasicRMLScreen, bases<GameScreen>, boost::shared_ptr<BasicRMLScreenWrap>,
boost::noncopyable>("BasicRMLScreen", init<const std::string&, const std::string&, Engine*, int>())
.def("HandleKeyPressed",&BasicRMLScreen::HandleKeyPressed,&BasicRMLScreenWrap::HandleKeyPressedDefault)
;
the problem is that when I wrap it like this, I get the following error:
Error 74 error C2664: 'boost::mpl::assertion_failed' : cannot convert parameter 1
from 'boost::mpl::failed ************boost::mpl::or_<T1,T2>::* ***********' to
'boost::mpl::assert<false>::type'
if I switch boost::ref(iaction) to iaction it compiles fine, but I need to pass
it by ref for correct behaviour. I'm not sure if this is a boost::ref problem
or a boost python issue but was curious if someone might have an idea how to
correct it. I can pass using boost:ref fine in the other places ive used it
with call_method. Is this is an issues because it's an enum?
Any help would be appreciated,
I'm afraid you're run into a bit of an impossible problem. Boost.Python
only defines rvalue from-python converters for enums, and this actually
makes sense - like int, float, and str in Python, enums are immutable
Python objects; when you set them, you're really just assigning the name
of the variable to a new object. There's really no way to express
modifying an argument in-place in Python when the argument is an
immutable object.
I think you'll manually have to transform the signature to return the
new enum value in Python (i.e. make a derived class that implements the
enum ref virtual member function by delegating to a new enum-returning
virtual member function that you can wrap).
Jim
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