On 9/6/06, Alex Mohr <amohr@pixar.com> wrote:
This code allowed the setObject(None) to work now. Unfortunately it broke the functionality that had been working where I could call setObject(PythonObject).
More details (extracted from above):
I have:
// set method void setObject(ptr<Base> obj);
// Implicit conversion for ref_ptr to ptr bp::implicitly_convertible< ref_ptr<Base>, ptr<Base> );
// From original e-mail: this works to automatically convert // ptr<Base> returns into ref_ptr<Base> as the held type bp::to_pyton_converter< ptr<Base>, ptr_to_python< ptr<Base> >()
// Most recent discussion: way to get None from python as ptr<Base> // - This works to let me pass None into wrapped setObject method bp::converter::registry::insert(&convertible, &construct, bp::type_id<ptr<Base> >());
The problem is that now when I try to call something like this in python:
new_obj = objtype.create() setObject(None) setObject(new_obj)
Both of these calls to setObject try to convert the object to a ptr<Base> using the manually registered converter. The converter only really knows how to deal with the conversion from a None type. In the case of a real object I just want boost.python to convert the held type (ref_ptr<Base> ) into a ptr<Base> using the implicit conversion.
How do I get this to work? Can I have multiple converters registered and if so how do I tell boost.python to only use the manually created one for the NoneType?
The rvalue converter should handle both cases. In convertible, it checks if it is getting None -- if it is, it says yes, I can make a pointer. If it gets something other than None, it says I can make a pointer iff I can get an lvalue pointer to the Pointee from the python object. That's the code after the if. It uses already registered lvalue converters to do this.
The construct method has a similar structure -- in the None case (first part of if) it will just placement new a default-constructed pointer. In the else part of the if, it will placement new a pointer pointing to the c++ instance.
Can you tell me what's going on in convertible and construct when you do this?
The problem for me was that the rvalue converter when passed a non-None could not do the placement new created of the ptr<Base> because the constructor is protected. The library I am wrapping requires all objects to be created using static factory methods: ref_ptr<Base> obj = Class.create() So there is something going on in the implicit conversion for the smart pointers that just handles things better. I ended up getting the code to work though by making it so the rvalue convertible method return NULL if p != NonType. This ends up meaning that the rvalue converter is only used in the case of passing None, but it works for me now. Thanks for your help. I will let you know if anything else crops up but I think I am starting to understand this part of boost.python much better now so hopefully I will be able to fix it myself. :) Thanks, Allen
setObject(new_obj)
Alex
template <class Ptr> struct smart_ptr_from_python { typedef typename boost::python::pointee<Ptr>::type Pointee; smart_ptr_from_python() { converter::registry::insert(&convertible, &construct, type_id<Ptr>()); } private: static void *convertible(PyObject *p) { // can always produce a pointer from None. if (p == Py_None) return p; // Otherwise, we can do it if we can get the pointee out. void *result = converter::get_lvalue_from_python (p, converter::registered<Pointee>::converters); return result; }
static void construct(PyObject* source, converter:: rvalue_from_python_stage1_data* data) { void* const storage = ((converter::rvalue_from_python_storage<Ptr>*)data)-> storage.bytes; // Deal with the "None" case. if (data->convertible == source) new (storage) Ptr(); // Or whatever you want. else new (storage) Ptr(static_cast<Pointee*>(data->convertible)); data->convertible = storage; } };
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