Exporting wrapped functions doesn't work

Open
#466 0 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
38/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
cpp
Domain
api

Research direction

Start by reproducing the wrapped-function examples in the issue, then inspect the boost::python::def entry point and its handling of callable objects. Done means the wrapped add2 and add examples can be exported successfully, matching the cases that already work directly.

Written by the indexing model from the issue text.

Description

I find myself in need of exporting a whole lot of functions to Python which require a wrapper (the API needs locking and whatnot).

The following code probably should work (pybind11 can handle it, for the most part), but doesn't.

#include <iostream>
#include <boost/python.hpp>

template <class R, class... Args>
struct wrap
{
    using funct_type = R(*)(Args...);
    funct_type func;
    wrap(funct_type f): func(f) {};
    R operator()(Args&&... args)
    {
          std::cout << "before calling\n";
          R ret=func(std::forward<Args>(args)...);
          std::cout << "After calling\n";
          return ret;
    }
};

class bar {};
class foo : bar {
    public:
    enum xfoo { FOO=1, BAR=2, BAZ=3    };
    static int add(int a, int b, enum xfoo c) { return a+b; }
    static int add2(int a, int b) { return a+b; }
};

BOOST_PYTHON_MODULE(example)
{
    using namespace boost::python;

    // this works
    std::cout << "Result" << wrap{foo::add}(1,2, foo::xfoo::FOO) << std::endl;

    // so does this
    def("add", foo::add, "A function that adds two numbers and no enum");

    // this works with pybind11 but not boost
    def("add2", wrap{foo::add2}, "A function that adds two numbers");

    // this works with neither
    def("add", wrap{foo::add}, "A function that adds two numbers and no enum");
}
Dominant language
C++
Stars
537
Forks
223
Avg merge
11h 22m
Merged PRs (30d)
2

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from boostorg/python

All issues in boostorg/python

Similar issues

More C++ issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.