Boost.Python library build errors when no default constructor and unique pointer

Question

I am trying to wrap my C++ code using Boost.Python and have encountered a couple errors and could use some help at solving them. But first here are the assets I have.

Product.h

namespace Products
{
  class Product
  {
  public:
    virtual ~Product() {};
    virtual int generateProduct(int verbose = 0) = 0;
    virtual int getQueueNum() = 0;
    virtual std::vector<std::vector<std::string> > getQueue(const int &index_int) = 0;
  };
}

ProductBuilder.h

namespace Products
{
  class ProductBuilder
  {
  public:
    ProductBuilder(const std::map<std::string,std::string> input_map, const std::deque<std::string> &dates_deque);
    int build(int verbose = 0);
    int numQueue() {return m_product->getQueueNum();};
    std::vector<std::vector<std::string> > getQueueByIndex(const int &index_int) {return m_product->getQueue(index_int);};
  private:
    std::unique_ptr<Products::Product> m_product;
  };
}

full-wrapper.cpp

BOOST_PYTHON_MODULE(alucard)
  {
    class_<Products::ProductBuilder>("ProductBuilder", init<std::map<std::string,std::string>,std::deque<std::string>>())
    .def("build", &Products::ProductBuilder::build)
    .def("numQueue", &Products::ProductBuilder::numQueue)
    .def("getQueueByIndex", &Products::ProductBuilder::getQueueByIndex)
    ;
  }

The errors that I am getting when I build the library via cmake are as follows:

/usr/include/boost/python/object/value_holder.hpp:133:13: error: use of deleted function ‘Products::ProductBuilder::ProductBuilder(const Products::ProductBuilder&)’
             BOOST_PP_REPEAT_1ST(N, BOOST_PYTHON_UNFORWARD_LOCAL, nil)
             ^
In file included from /home/jlahowetz2/development/cpp-python-wrapper/full-wrapper.cpp:11:0:
/data/alucard/include/ProductBuilder.h:25:9: note: ‘Products::ProductBuilder::ProductBuilder(const Products::ProductBuilder&)’ is implicitly deleted because the default definition would be ill-formed:
   class ProductBuilder
         ^~~~~~~~~~~~~~
/data/alucard/include/ProductBuilder.h:25:9: error: use of deleted function ‘std::unique_ptr<_Tp, _Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = Products::Product; _Dp = std::default_delete<Products::Product>]’
In file included from /usr/include/c++/7/memory:80:0,
                 from /usr/include/boost/function/function_base.hpp:16,
                 from /usr/include/boost/function/detail/prologue.hpp:17,
                 from /usr/include/boost/function/function_template.hpp:13,
                 from /usr/include/boost/function/detail/maybe_include.hpp:13,
                 from /usr/include/boost/function/function0.hpp:11,
                 from /usr/include/boost/python/errors.hpp:13,
                 from /usr/include/boost/python/handle.hpp:11,
                 from /usr/include/boost/python/args_fwd.hpp:10,
                 from /usr/include/boost/python/args.hpp:10,
                 from /usr/include/boost/python.hpp:11,
                 from /home/jlahowetz2/development/cpp-python-wrapper/full-wrapper.cpp:1:
/usr/include/c++/7/bits/unique_ptr.h:383:7: note: declared here
       unique_ptr(const unique_ptr&) = delete;
       ^~~~~~~~~~

H. Guijt · Accepted Answer · 2021-01-28 23:16:57Z

1

+50

Apparently the Python code copies your ProductBuilder object. However, ProductBuilder contains a unique_ptr, which cannot be copied (it can only be moved). One easy way to fix this is to replace the unique_ptr by a shared_ptr, which is copyable.

answered Jan 28, 2021 at 23:16

H. Guijt

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1 Comment

deadpickle Over a year ago

Think you were right, adding class_<Products::ProductBuilder, boost::noncopyable> caused it to compile but now I cant import the code into python since it returns a segfault

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