将 unique_ptr 与 boost python 结合使用 - boost::shared_ptr 有效，但 unique_ptr 无效

这可能与以下问题相同

Boost Python 没有 to_python for std::unique_ptr https://stackoverflow.com/questions/20590205/boost-python-no-to-python-for-stdunique-ptr

但是，我还没有看到回复，也不清楚这是一个“boost-python”问题还是由于我对“std::unique_ptr”的特殊使用 我试图弄清楚为什么在使用“std::unique_ptr []”时更改从 boost::shared_ptr 派生的类会中断编译

下面是我的 boost python 模块，有 2 个可能的“smart_array”类 原始版本基于 boost::shared_array 并且工作正常（如下所示）

当我使用基于 unique_ptr （简单替换）的一个时，我会遇到令人困惑的编译错误。

// Boost Includes ==============================================================
#include <boost/python.hpp>
#include <boost/cstdint.hpp>

#define NO_BOOST
#ifdef NO_BOOST
#include "smart_array.h"
#else
#include "boost_smart_array.h"
#endif
template <class Numeric> class cic {
public:
        smart_array<Numeric> nacc; //! Accumulators
        cic(int s) :  nacc(3) {
                for (int i=0;i<3;i++) nacc[i] = (Numeric)0;
        }
        Numeric interpolate() {         return(nacc[2]);        }
};

// Using =======================================================================
using namespace boost::python;
BOOST_PYTHON_MODULE(cic_double)
{
        class_< cic<double> >("cic_double", init< int >())
                .def("interpolate", &cic<double>::interpolate);
}

-- 智能数组类（原-boost）

#include "boost/shared_array.hpp"
    template<class T> class smart_array : public boost::shared_array<T> {
    public:
            //! Default constructor
            smart_array() {} 
            //! Create an smart_array of size n
            smart_array(long n) : boost::shared_array<T>(new T[n]) {
                    elements = n;
            }
            void resize(long n) { 
                    elements = n;
                    boost::shared_array<T>::reset(new T[n]); 
            }
            long len() const { return(elements); }
    private:
            long elements;
    };

新的-基于unique_ptr

template<class T> class smart_array : public std::unique_ptr<T []> {
 public:
  //! Default constructor
  smart_array() {} 
  //! Create an smart_array of size n
  smart_array(long n) : std::unique_ptr<T []>(new T[n]) {
                elements = n;
  }
  void resize(long n) { 
                elements = n;
                std::unique_ptr<T []>::reset(new T[n]); 
  }
  long len() const { return(elements); }
 private:
  long elements;
};

编译错误

[100%] Building CXX object CMakeFiles/cic_double.dir/py_cic_double.cpp.o
In file included from /Users/user/GitHubStuff/boost_cic_test/py_cic_double.cpp:2:
In file included from /usr/local/include/boost/python.hpp:18:
In file included from /usr/local/include/boost/python/class.hpp:23:
In file included from /usr/local/include/boost/python/object/class_metadata.hpp:11:
In file included from /usr/local/include/boost/python/object/value_holder.hpp:50:
In file included from /usr/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:52:
/usr/local/include/boost/python/object/value_holder.hpp:135:11: error: no matching constructor for initialization of 'cic<double>'
        : m_held(
          ^
/usr/local/include/boost/python/object/make_instance.hpp:71:30: note: in instantiation of function template specialization 'boost::python::objects::value_holder<cic<double> >::value_holder<boost::reference_wrapper<const cic<double> > >' requested here
        return new (storage) Holder(instance, x);
                             ^
/usr/local/include/boost/python/object/make_instance.hpp:45:22: note: in instantiation of member function 'boost::python::objects::make_instance<cic<double>, boost::python::objects::value_holder<cic<double> > >::construct' requested here
            Derived::construct(&instance->storage, (PyObject*)instance, x)->install(raw_result);
                     ^
/usr/local/include/boost/python/object/class_wrapper.hpp:29:30: note: in instantiation of function template specialization 'boost::python::objects::make_instance_impl<cic<double>, boost::python::objects::value_holder<cic<double> >, boost::python::objects::make_instance<cic<double>, boost::python::objects::value_holder<cic<double> > > >::execute<const boost::reference_wrapper<const cic<double> > >' requested here
        return MakeInstance::execute(boost::ref(x));
                             ^
/usr/local/include/boost/python/converter/as_to_python_function.hpp:27:72: note: in instantiation of member function 'boost::python::objects::class_cref_wrapper<cic<double>, boost::python::objects::make_instance<cic<double>, boost::python::objects::value_holder<cic<double> > > >::convert' requested here
        convert_function_must_take_value_or_const_reference(&ToPython::convert, 1L);
                                                                       ^
/usr/local/include/boost/python/to_python_converter.hpp:88:22: note: in instantiation of member function 'boost::python::converter::as_to_python_function<cic<double>, boost::python::objects::class_cref_wrapper<cic<double>, boost::python::objects::make_instance<cic<double>, boost::python::objects::value_holder<cic<double> > > > >::convert' requested here
        &normalized::convert
                     ^
/usr/local/include/boost/python/object/class_wrapper.hpp:24:8: note: (skipping 2 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
struct class_cref_wrapper
       ^
/usr/local/include/boost/python/object/class_metadata.hpp:219:25: note: in instantiation of function template specialization 'boost::python::objects::class_metadata<cic<double>, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>::register_aux2<cic<double>, boost::integral_constant<bool, false> >' requested here
        class_metadata::register_aux2((T*)0, use_callback());
                        ^
/usr/local/include/boost/python/object/class_metadata.hpp:205:25: note: in instantiation of member function 'boost::python::objects::class_metadata<cic<double>, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>::register_aux' requested here
        class_metadata::register_aux((T*)0);
                        ^
/usr/local/include/boost/python/class.hpp:497:19: note: in instantiation of member function 'boost::python::objects::class_metadata<cic<double>, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>::register_' requested here
        metadata::register_(); // set up runtime metadata/conversions
                  ^
/usr/local/include/boost/python/class.hpp:209:15: note: in instantiation of function template specialization 'boost::python::class_<cic<double>, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>::initialize<boost::python::init_base<boost::python::init<int, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_> > >' requested here
        this->initialize(i);
              ^
/Users/user/GitHubStuff/boost_cic_test/py_cic_double.cpp:24:2: note: in instantiation of function template specialization 'boost::python::class_<cic<double>, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>::class_<boost::python::init<int, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_, mpl_::void_> >' requested here
        class_< cic<double> >("cic_double", init< int >())
        ^
/Users/user/GitHubStuff/boost_cic_test/py_cic_double.cpp:11:32: note: candidate constructor (the implicit copy constructor) not viable: 1st argument ('typename reference_wrapper<const cic<double> >::type' (aka 'const cic<double>')) would lose const qualifier
template <class Numeric> class cic {
                               ^
/Users/user/GitHubStuff/boost_cic_test/py_cic_double.cpp:14:2: note: candidate constructor not viable: no known conversion from 'typename reference_wrapper<const cic<double> >::type' (aka 'const cic<double>') to 'int' for 1st argument
        cic(int s) :  nacc(3) {
        ^
1 error generated.
make[3]: *** [CMakeFiles/cic_double.dir/py_cic_double.cpp.o] Error 1
make[2]: *** [CMakeFiles/cic_double.dir/all] Error 2
make[1]: *** [all] Error 2
make: *** [all] Error 2

遗憾的是，目前还无法曝光std::unique_ptr使用 boost::python，因为它需要移动语义，而 boost::python 尚不支持这些（更多详细信息here https://stackoverflow.com/questions/20581679/boost-python-how-to-expose-stdunique-ptr）。此外，您不应该从智能指针派生，因为它是这不是一个好的做法 https://stackoverflow.com/questions/3801648/why-doesnt-shared-ptr-have-a-virtual-descructor-and-how-can-i-get-around-this并且它们没有虚拟析构函数（除了许多其他原因）

话虽如此，您还有很多其他选择，其中一些是：

• use std::auto_ptr作为数据成员，这得到了很好的支持boost::python（假设您的课程不可复制）。然而，一个auto_ptr无法容纳数组（它不会调用正确的变体delete()).
• use boost::shared_ptr作为数据成员，并在 API 中隐藏其使用。但是，请注意boost::shared_ptr 不能不保存数组数据 https://stackoverflow.com/questions/13061979/shared-ptr-to-an-array-should-it-be-used出于与上述相同的原因。
• wrap an std::vector<boost::shared_ptr<>>，这将与boost::shared_ptr开箱即用矢量索引套件 http://www.boost.org/doc/libs/1_42_0/libs/python/doc/v2/indexing.html.
• ...以及许多其他人。

然而，还有很多其他方法，我个人建议重新设计代码，以使用 boost::python 示例中一些更普遍接受的编码和 python 包装实践。