Question

I get some compile time errors and I can’t understand why that is. The following code will refuse to compile, giving me the following errors:

error C2664: ‘void (PyObject *,const char *,boost::type *)’ : cannot convert parameter 1 from ‘const char *’ to ‘PyObject *’
error C2664: ‘void (PyObject *,const char *,boost::type *)’ : cannot convert parameter 3 from ‘boost::shared_ptr’ to ‘boost::type *’

PyObject* self = ...;
const char* fname = "...";
boost::function<void (boost::shared_ptr<Event>)> func;
func = boost::bind(boost::python::call_method<void>, self, fname, _1);

Answer 1

boost::python::call_method consists of several overloaded functions that take a different number of arguments, defined like this:

template <class R>
R call_method(PyObject* self, char const* method);
template <class R, class A1>
R call_method(PyObject* self, char const* method, A1 const&);
template <class R, class A1, class A2>
R call_method(PyObject* self, char const* method, A1 const&, A2 const&);
...

When you call it directly (e.g. call_method<void>(self, name, arg1, arg2)), the compiler can choose the correct overload and templated argument types automatically. But when you pass a function pointer to call_method into bind, you need to manually specify the overload and argument types, by using:

call_method<ReturnType, Arg1Type, Arg2Type, ...>

Or in this case:

call_method<void, boost::shared_ptr<Event> >