issue with unique_ptr ?

[jkhoogland]

Hi,

I came across the following issue today which seems like a bug.

I have a class Foo that produces Bar and returns a unique_ptr to an instance of Bar.

On running a C++11 executable it works fine (little main in the code attached).
On running python, it craps out with

RuntimeError: return_value_policy = move, but the object is neither movable nor copyable!

Am I missing something ? The class Bar is moveable, and copyable...

Code attached to reproduce.

pybind11_issue_unique_ptr.zip

[dean0x7d]

This should be fixed in PR #607. Fixing this wasn't the goal of that PR, but it does seem to be a lucky side effect.

[jkhoogland]

cool, i'll wait for it to hit master
thanks for the quick update

[jkhoogland]

Hi,
I created a branch to test your changes, the initial error

RuntimeError: return_value_policy = move, but the object is neither movable nor copyable!

is gone but I now see a different error popping up:

Failed to import pybind11_tests from pytest:
 ImportError: generic_type: cannot initialize type "Foo": an object with that name is already defined

I dont think that there is anything wrong in my py module declaration:

test_initializer unique_ptr( []( py::module& m ) {

 py::class_<FooI, std::unique_ptr<FooI>> foo( m, "FooI" );
 foo.def( "bar", &FooI::bar );

 py::class_<Foo, std::unique_ptr<Foo>>( m, "Foo", foo )
 .def( py::init<>() );

 py::class_<BarI, std::unique_ptr<BarI>> bar( m, "BarI" );
 foo.def( "bla", &BarI::bla );

 py::class_<Bar, std::unique_ptr<Bar>>( m, "Bar", bar )
 .def( py::init<int>() );

} );

Any thoughts ?
Regards
Jiri

[dean0x7d]

Based on

test_initializer unique_ptr( []( py::module& m ) { ... }

I'm guessing you're trying this out alongside the exisitng pybind11 tests. But those already have a class called Foo, hence the duplicate initialization error.

[jagerman]

If that is indeed it, cmake -DPYBIND_TEST_OVERRIDE=test_mine.cpp can be helpful for turning off compilation of everything except for one test cpp file. (I also use it all the time when working on one particular feature to cut down compilation/link times).

[jkhoogland]

Right, sorry about that, indeed a stupid mistake.
I also forgot to add the test code i wrote, which I submitted now to my test branch.

Having fixed that though, I do see an issue that I think is a bug:

The two classes Foo and Bar are as defined above.

Running

from pybind11_tests import (Bar, Foo)

print("dir(Foo):\n",dir(Foo))
print("dir(Bar):\n",dir(Bar))

foo = Foo()
bar = foo.bar()

print(type(foo))
print(type(bar))

print(bar.bla())

gives some surprising output:

dir(Foo):
 ['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'bar', 'bla']
dir(Bar):
 ['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']
<class 'pybind11_tests.Foo'>
<class 'pybind11_tests.Bar'>

and then it barfs since it cannot find the method bla on Bar.
Looking at the output of dir(Foo) it is seen that pybind11 has put the method bla on Foo...

This looks like there is something going wrong in parsing the interface when wrapping the c++ code in pybind11 ?

[jagerman]

This looks suspect:

 py::class_<BarI, std::unique_ptr<BarI>> bar( m, "BarI" );
 foo.def( "bla", &BarI::bla );

bla is defined as a bound method on Foo, but then bound to a function of BarI. Thus when pybind11 tries to dispatch foo.bla() it will see that bla has one entry with first argument type BarI, but you gave it a first argument of type Foo, so it won't match.

[jkhoogland]

ouch, sorry for that stupidity, yep, problem solved.
Thanks for your help and patience

dir(Foo):
 ['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'bar']
dir(Bar):
 ['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'bla']
<class 'pybind11_tests.Foo'>
<class 'pybind11_tests.Bar'>
123