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pybind11-utils

This library contains some utility stuff for pybind11

smart_variant_wrapper.h

Expose a function mo2::python::wrap_arguments and a template mo2::python::smart_variant that can be used to expose more interesting types Python than the C++ one, e.g., accept os.PathLike and QFileInfo when a simple QString is expected.

A toy example can be found in the test folder at tests/python/test_argument_wrapper.cpp.

More concrete examples can be found in mobase/pybind11_all.h for FileWrapper and DirectoryWrapper.

functional.h

TODO: updated version of <pybind11/functional.h> that should check the signature a bit more when creating std::function (similar to previous implementation).

shared_cpp_owner.h

Expose a macro MO2_PYBIND11_SHARED_CPP_HOLDER that can be used to declare that std::shared_ptr<...> must hold-on their associate Python object.

// use the macro on the type to be exposed (with a trampoline class)
MO2_PYBIND11_SHARED_CPP_HOLDER(ISaveGame)

// use std::shared_ptr<> as the holder for the class
py::class_<ISaveGame, PySaveGame, std::shared_ptr<ISaveGame>>(...);

Using the MO2_PYBIND11_SHARED_CPP_HOLDER (must be present in all files manipulating ISaveGame between C++ and Python) ensure that the Python instance remains alive alongside the C++ one.

The MO2_PYBIND11_SHARED_CPP_HOLDER declares a specialization of type_caster<> that alters the std::shared_ptr by return a std::shared_ptr<> that owns the Python object (via a pybind11::object) but does not release the C++ one - The C++ object is owned by the Python one, so the relation is as follows:

  • The std::shared_ptr<X> manipulated in C++ maintains the pybind11::object alive through a custom deleter but DOES NOT release the C++ object when the reference count reaches 0.
  • The Python object holds a standard std::shared_ptr<X> that will release the object when the reference count reaches 0.