pybind11/docs/limitations.rst
Henry Schreiner e4e5c49a26
docs: known issues (#2565)
* docs: FAQ CMake updates

* docs: limitations

* ci: don't over label

* docs: update CHANGELOG, add a bit more structure

* ci: label PRs with more labels, and sooner

* docs: updates from @rwgk

* docs: address @YannickJadoul's points
2020-10-09 11:19:13 -04:00

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Limitations
###########
Design choices
^^^^^^^^^^^^^^
pybind11 strives to be a general solution to binding generation, but it also has
certain limitations:
- pybind11 casts away ``const``-ness in function arguments and return values.
This is in line with the Python language, which has no concept of ``const``
values. This means that some additional care is needed to avoid bugs that
would be caught by the type checker in a traditional C++ program.
- The NumPy interface ``pybind11::array`` greatly simplifies accessing
numerical data from C++ (and vice versa), but it's not a full-blown array
class like ``Eigen::Array`` or ``boost.multi_array``. ``Eigen`` objects are
directly supported, however, with ``pybind11/eigen.h``.
Large but useful features could be implemented in pybind11 but would lead to a
significant increase in complexity. Pybind11 strives to be simple and compact.
Users who require large new features are encouraged to write an extension to
pybind11; see `pybind11_json <https://github.com/pybind/pybind11_json>`_ for an
example.
Known bugs
^^^^^^^^^^
These are issues that hopefully will one day be fixed, but currently are
unsolved. If you know how to help with one of these issues, contributions
are welcome!
- The test suite currently segfaults on macOS and Python 3.9.0 when exiting the
interpreter. This was suspected to be related to the cross module GIL code,
but could be a broader Python 3.9.0 issue.
`#2558 <https://github.com/pybind/pybind11/issues/2558>`_
- The ``cpptest`` does not run on Windows with Python 3.8 or newer, due to DLL
loader changes. User code that is correctly installed should not be affected.
`#2560 <https://github.com/pybind/pybind11/pull/2560>`_
- There may be a rare issue with leakage under some compilers, exposed by
adding an unrelated test to the test suite.
`#2335 <https://github.com/pybind/pybind11/pull/2335>`_
Known limitations
^^^^^^^^^^^^^^^^^
These are issues that are probably solvable, but have not been fixed yet. A
clean, well written patch would likely be accepted to solve them.
- Type casters are not kept alive recursively.
`#2527 <https://github.com/pybind/pybind11/issues/2527>`_
One consequence is that containers of ``char *`` are currently not supported.
`#2245 <https://github.com/pybind/pybind11/issues/2245>`_