Ah, I see! That does the trick! Thank you very much. I was clearly
confused about what "caller_owns_return" meant -- I had it backwards.
Mike.
On Jun 22, 2009, at 5:11 PM, Gustavo Carneiro wrote:
2009/6/22 J. Michael Owen <mikeo...@llnl.gov>
I'm looking at wrapping a C++ singleton with pybindgen, and it seems
that if I expose the method for getting the instance to python the
generated code wants to call a copy constructor, which seems wrong
to me. If for instance I define a class "A" as a singleton:
class A {
public:
static A* instancePtr() {
if (A::mInstancePtr == 0) A::mInstancePtr = new A;
return mInstancePtr;
}
private:
A();
A(const A& rhs);
A& operator=(const A& rhs);
static A* mInstancePtr;
};
and I wrap A and its instance method like so:
mod = Module("singleton_example")
mod.add_include('"singleton_example.hh"')
x = mod.add_class("A", is_singleton=True)
x.add_method("instancePtr", retval("A*", caller_owns_return=False),
[])
pybindgen generates the following code for the instancePtr method:
PyObject *
_wrap_PyA_instancePtr(PyA *self)
{
PyObject *py_retval;
A *retval;
PyA *py_A;
retval = self->obj->instancePtr();
if (!(retval)) {
Py_INCREF(Py_None);
return Py_None;
}
py_A = PyObject_New(PyA, &PyA_Type);
py_A->obj = new A(*retval);
py_retval = Py_BuildValue((char *) "N", py_A);
return py_retval;
}
As you can see it is trying to construct a new object with a copy of
the A retval parameter (the line that reads "py_A->obj = new
A(*retval);". This is of course forbidden because all of A's
constructors are private -- as a singleton we don't want anyone
calling constructors on this object. Moreover, since I exposed
"instancePtr" as returning a pointer I did not expect any copies to
be generated anyway -- I'd like to see the pointer "retval" sent
back directly (even if this wasn't a singleton). Am I missing some
syntax here to prevent pybindgen from trying to make these copies?
It tries to copy because you say caller_owns_return=False, pybindgen
needs to copy the object so that the wrapper can own the object.
What you can do here is use caller_owns_return=True instead of
False. It's OK in this case; because of the is_singleton option,
the C++ wrapped object will never be freed when the wrapper is
destroyed.
--
Gustavo J. A. M. Carneiro
INESC Porto, Telecommunications and Multimedia Unit
"The universe is always one step beyond logic." -- Frank Herbert
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