Failing to build python bindings

[SomeoneSerge]

Hi! Built the tests fine, but gcc doesn't seem to like the signatures in the python bindings

error: invalid 'static_cast' from type '<unresolved overloaded function type>' to type 'std::string (*)(const xt::pytensor<double, 1, xt::layout_type::dynamic>&)' {aka 'std::__cxx11::basic_string<char> (*)(const xt::pytensor<dou
       │ ble, 1, xt::layout_type::dynamic>&)'}
  69   │    61 |         static_cast<std::string (*)(const xt::pytensor<double, 1>&)>(&cppcolormap::rgb2hex),

Logs: https://gist.github.com/SomeoneSerge/2507244e5bc3b11982948ff0ed86a681
Getting the same error with gcc11 and gcc12.
Pybind11 version: pybind11-2.10.3/include (found version "2.10.3")
Built with: SomeoneSerge/pkgs@b0274d7

[tdegeus]

Thanks! I tried debugging here #38 but unfortunately the CI works fine on Linux GCC 11.3.0. This makes it a bit harder to understand what is bugging the compiler and to solve it. It seems that the compiler has a hard time deciding between

template <class T, typename std::enable_if_t<xt::get_rank<T>::value != 1, int> = 0>
std::vector<std::string> rgb2hex(const T& arg);

template <class T, typename std::enable_if_t<xt::get_rank<T>::value == 1, int> = 0>
std::string rgb2hex(const T& arg);

Could you tried by adding the template explicitly to main.cpp:

    m.def(
        "rgb2hex",
        static_cast<std::string (*)(const xt::pytensor<double, 1>&)>(&cppcolormap::rgb2hex<xt::pytensor<double, 1>>),
        DOC("rgb2hex")
    );

    m.def(
        "rgb2hex",
        static_cast<std::vector<std::string> (*)(const xt::pytensor<double, 2>&)>(
            &cppcolormap::rgb2hex<xt::pytensor<double, 2>>
        ),
        DOC("rgb2hex")
    );

?
Thanks!

[SomeoneSerge]

Quick update: still getting the same error at the first overload, i.e. one that returns std::string rather than a vector. The second one compiles. By the way, shouldn't the first one also consume a pytensor? Like pytensor<double, 1> (edit: I see it already does) To be precise, here's the full diff I tried: https://github.com/SomeoneSerge/cppcolormap/pull/1/files

TODO: I should compare xtensor and pybind11 versions, and maybe set up a separate gh action to reproduce the failures more easily

[tdegeus]

Thanks for the update. That help to narrow it down. If I read better it seems that the compiler converts the std::string to std::__cxx11::basic_string<char> and then is naturally confused. Maybe #41 helps? Otherwise this might be a useful reference https://stackoverflow.com/questions/40705852/undefined-reference-to-std-cxx11basic-string-in-boost-on-travis-ci .

[SomeoneSerge]

No, that doesn't help yet, and I don't think it's got anything to do with cxx11 abi: the vector of strings seems to be fine.
By the way, I get this warning from ccls:

address of overloaded function 'rgb2hex' cannot be static_cast to type 'std::string (*)(const xt::pytensor<double, 1> &)' (aka 'basic_string<char> (*)(const pytensor<double, 1> &)')

[tdegeus]

Just to be sure, are you on xtensor-python >=0.25.2 ?

[SomeoneSerge]

0.25.1

[tdegeus]

Then problem solved. xt::pytensor only has the static rank property since 0.25.2 (see xtensor-stack/xtensor-python#241 ) . So pre-0.25.2 the compiler throws out

cppcolormap/include/cppcolormap.h

Line 245 in 2fe9454

template <class T, typename std::enable_if_t<xt::get_rank<T>::value == 1, int> = 0>

[tdegeus]

For future reference 2fe9454

[SomeoneSerge]

Perfect, thanks! Maybe also a VERSION in find_package?

EDIT: I'll test with a newer xtensor and close the issue if that works out

[tdegeus]

Perfect, thanks! Maybe also a VERSION in find_package?

Sounds great, a PR is welcome

[SomeoneSerge]

xtensor-python 0.26.1, works like a charm

Frankly though, maybe 0.25.2 deserved at least a minor version bump, not just the patch version 😆

[tdegeus]

xtensor*'s versioning is a mystery to me ;)