boostpython：使用return\u internal\u引用将参数的生存期绑定到返回值

我开始学习使用boostpython，并提出了一个新手问题

我想编写一个函数，将其参数的生存期与其结果联系起来，这样当我调用

r=func（a）

时，如果我仍然有

r

的引用，则参数

a

将永远不会被销毁。文档建议对此类请求使用

return\u internal\u reference

call策略。但这是否要求

r

作为

a

的内部参考，正如名称所示

在下面的（过于简化的）示例中，假设我想将输入数组

a

的生存期与生成的lambda函数联系起来，该函数不是输入

a

的内部引用

#include <functional>
#include <boost/python.hpp>
#include <boost/python/return_internal_reference.hpp>

using namespace std;
using namespace boost::python;

function<float(int)> func(const float* a) {
  return [=](int n) { return a[n]; };
}

BOOST_PYTHON_MODULE(test) {
  def("func", func, return_internal_reference<1>());
}

当我试图编译上面的代码时，下面列出了一大堆错误，但是如果我删除

return\u internal\u reference（）

call策略，代码编译成功

我很确定我使用这个呼叫策略是错误的，但不确定如何使它正确。任何指针都将受到高度赞赏。非常感谢

$ g++ -std=c++11 -shared Test.cc -I/opt/local/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -L/opt/local/lib -lboost_python-mt -lpython2.7 -o test.so
In file included from /opt/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:52:0,
                 from /opt/local/include/boost/python/detail/invoke.hpp:63,
                 from /opt/local/include/boost/python/detail/caller.hpp:16,
                 from /opt/local/include/boost/python/object/function_handle.hpp:8,
                 from /opt/local/include/boost/python/converter/arg_to_python.hpp:19,
                 from /opt/local/include/boost/python/call.hpp:15,
                 from /opt/local/include/boost/python/object_core.hpp:14,
                 from /opt/local/include/boost/python/args.hpp:25,
                 from /opt/local/include/boost/python.hpp:11,
                 from Test.cc:2:
/opt/local/include/boost/python/detail/invoke.hpp: In instantiation of 'PyObject* boost::python::detail::invoke(boost::python::detail::invoke_tag_<false, false>, const RC&, F&, AC0&) [with RC = boost::python::detail::reference_existing_object_requires_a_pointer_or_reference_return_type<std::function<float(int)> >; F = std::function<float(int)> (*)(const float*); AC0 = boost::python::arg_from_python<const float*>; PyObject = _object]':
/opt/local/include/boost/python/detail/caller.hpp:223:13:   required from 'PyObject* boost::python::detail::caller_arity<1u>::impl<F, Policies, Sig>::operator()(PyObject*, PyObject*) [with F = std::function<float(int)> (*)(const float*); Policies = boost::python::return_internal_reference<>; Sig = boost::mpl::vector2<std::function<float(int)>, const float*>; PyObject = _object]'
/opt/local/include/boost/python/object/py_function.hpp:38:33:   required from 'PyObject* boost::python::objects::caller_py_function_impl<Caller>::operator()(PyObject*, PyObject*) [with Caller = boost::python::detail::caller<std::function<float(int)> (*)(const float*), boost::python::return_internal_reference<>, boost::mpl::vector2<std::function<float(int)>, const float*> >; PyObject = _object]'
Test.cc:14:1:   required from here
/opt/local/include/boost/python/detail/invoke.hpp:75:82: error: no match for call to '(const boost::python::detail::reference_existing_object_requires_a_pointer_or_reference_return_type<std::function<float(int)> >) (std::function<float(int)>)'
     return rc(f( BOOST_PP_ENUM_BINARY_PARAMS_Z(1, N, ac, () BOOST_PP_INTERCEPT) ));
                                                                                  ^
In file included from /opt/local/include/boost/python/object/function_handle.hpp:8:0,
                 from /opt/local/include/boost/python/converter/arg_to_python.hpp:19,
                 from /opt/local/include/boost/python/call.hpp:15,
                 from /opt/local/include/boost/python/object_core.hpp:14,
                 from /opt/local/include/boost/python/args.hpp:25,
                 from /opt/local/include/boost/python.hpp:11,
                 from Test.cc:2:
/opt/local/include/boost/python/detail/caller.hpp: In instantiation of 'static const PyTypeObject* boost::python::detail::converter_target_type<ResultConverter>::get_pytype() [with ResultConverter = boost::python::detail::reference_existing_object_requires_a_pointer_or_reference_return_type<std::function<float(int)> >; PyTypeObject = _typeobject]':
/opt/local/include/boost/python/detail/caller.hpp:240:19:   required from 'static boost::python::detail::py_func_sig_info boost::python::detail::caller_arity<1u>::impl<F, Policies, Sig>::signature() [with F = std::function<float(int)> (*)(const float*); Policies = boost::python::return_internal_reference<>; Sig = boost::mpl::vector2<std::function<float(int)>, const float*>]'
/opt/local/include/boost/python/object/py_function.hpp:48:35:   required from 'boost::python::detail::py_func_sig_info boost::python::objects::caller_py_function_impl<Caller>::signature() const [with Caller = boost::python::detail::caller<std::function<float(int)> (*)(const float*), boost::python::return_internal_reference<>, boost::mpl::vector2<std::function<float(int)>, const float*> >]'
Test.cc:14:1:   required from here
/opt/local/include/boost/python/detail/caller.hpp:102:109: error: 'struct boost::python::detail::reference_existing_object_requires_a_pointer_or_reference_return_type<std::function<float(int)> >' has no member named 'get_pytype'
         return create_result_converter((PyObject*)0, (ResultConverter *)0, (ResultConverter *)0).get_pytype();
                                                                                                             ^

$g++-std=c++11-shared Test.cc-I/opt/local/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7-L/opt/local/lib-lboost\u Python-mt-lpython2.7-o Test.so
在/opt/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:52:0中包含的文件中，
从/opt/local/include/boost/python/detail/invoke.hpp:63，
从/opt/local/include/boost/python/detail/caller.hpp:16，
从/opt/local/include/boost/python/object/function_handle.hpp:8，
从/opt/local/include/boost/python/converter/arg_到_python.hpp:19，
从/opt/local/include/boost/python/call.hpp:15，
从/opt/local/include/boost/python/object_core.hpp:14，
从/opt/local/include/boost/python/args.hpp:25，
从/opt/local/include/boost/python.hpp:11，
来自测试。cc:2：
/opt/local/include/boost/python/detail/invoke.hpp:PyObject*boost:：python:：detail:：invoke（boost:：python:：detail:：invoke\u tag，const RC&，F&，AC0&）实例化[with RC=boost:：python:：detail:：reference\u现有的\u对象需要\u指针\u或\u reference\u返回类型；F=std:：function（*）（const float*）；AC0=boost:：python:：arg_from_python；PyObject=_object]'：
/opt/local/include/boost/python/detail/caller.hpp:223:13:必须来自'PyObject*boost:：python:：detail:：caller_arity:：impl:：operator（）（PyObject*，PyObject*）[with F=std:：function（*）（const float*）；polics=boost:：python:：return_internal_reference；Sig=boost:：mpl:：vector2；PyObject=\u object]'
/opt/local/include/boost/python/object/py_function.hpp:38:33:必须来自“PyObject*boost:：python:：objects:：caller_py_function\u impl:：operator（）（PyObject*，PyObject*）[with caller=boost:：python:：detail:：caller；PyObject=\u object]”
测试。cc:14:1：从这里开始需要
/opt/local/include/boost/python/detail/invoke.hpp:75:82:错误：调用“（const boost:：python:：detail:：reference_现有_对象_需要_指针_或_引用_返回_类型）（std:：function）”不匹配
返回rc（f（BOOST_PP_ENUM_BINARY_PARAMS_Z（1，N，ac，（）BOOST_PP_INTERCEPT））；
^
在/opt/local/include/boost/python/object/function_handle.hpp:8:0中包含的文件中，
从/opt/local/include/boost/python/converter/arg_到_python.hpp:19，
从/opt/local/include/boost/python/call.hpp:15，
从/opt/local/include/boost/python/object_core.hpp:14，
从/opt/local/include/boost/python/args.hpp:25，
从/opt/local/include/boost/python.hpp:11，
来自测试。cc:2：
/opt/local/include/boost/python/detail/caller.hpp:static const PyTypeObject*boost:：python:：detail:：converter\u target\u type:：get\u pytype（）[with ResultConverter=boost:：python:：detail:：reference\u现有的\u对象\u需要\u指针\u或\u reference\u返回\u type；PyTypeObject=\u typeobject]：
/opt/local/include/boost/python/detail/caller.hpp:240:19:static boost:：python:：detail:：py\u func\u sig\u info boost:：python:：detail:：caller\u arity:：impl:：signature（）[with F=std:：function（*）（const float*）；Policies=boost:：python:：return\u internal\u reference；sig=boost:：mpl:：vector2]'
/opt/local/include/boost/python/object/py_function.hpp:48:35:来自“boost:：python:：detail:：py_func_sig_info boost:：python:：objects:：caller_py_function_impl:：signature（）const[with caller=boost:：python:：detail:：caller]'
测试。cc:14:1：从这里开始需要
/opt/local/include/boost/python/detail/caller.hpp:102:109:错误：“struct boost:：python:：detail:：reference_现有的_对象_需要_指针_或_reference_return_类型”没有名为“get_pytype”的成员
返回create_result_converter（（PyObject*）0，（ResultConverter*）0，（ResultConverter*）0；
^

考虑使用。此策略允许返回类型按值返回，同时仍将另一个对象的生存期延长至至少与返回对象的生存期相同

BOOST\u PYTHON\u模块（测试）{
def（“func”，func，带有监护权和监护权）；
}

---

如文档中所述，返回的对象引用现有的内部对象：

return\u internal\u reference

[…]允许安全返回指向内部持有的对象[…]的指针和引用，而无需复制引用对象

本文档还简要介绍了它与保管人和后调用的使用。总之，

return\u internal\u reference

对公开的函数有两个值得注意的影响：

• 那个人回来了

  $ g++ -std=c++11 -shared Test.cc -I/opt/local/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -L/opt/local/lib -lboost_python-mt -lpython2.7 -o test.so
  In file included from /opt/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:52:0,
                   from /opt/local/include/boost/python/detail/invoke.hpp:63,
                   from /opt/local/include/boost/python/detail/caller.hpp:16,
                   from /opt/local/include/boost/python/object/function_handle.hpp:8,
                   from /opt/local/include/boost/python/converter/arg_to_python.hpp:19,
                   from /opt/local/include/boost/python/call.hpp:15,
                   from /opt/local/include/boost/python/object_core.hpp:14,
                   from /opt/local/include/boost/python/args.hpp:25,
                   from /opt/local/include/boost/python.hpp:11,
                   from Test.cc:2:
  /opt/local/include/boost/python/detail/invoke.hpp: In instantiation of 'PyObject* boost::python::detail::invoke(boost::python::detail::invoke_tag_<false, false>, const RC&, F&, AC0&) [with RC = boost::python::detail::reference_existing_object_requires_a_pointer_or_reference_return_type<std::function<float(int)> >; F = std::function<float(int)> (*)(const float*); AC0 = boost::python::arg_from_python<const float*>; PyObject = _object]':
  /opt/local/include/boost/python/detail/caller.hpp:223:13:   required from 'PyObject* boost::python::detail::caller_arity<1u>::impl<F, Policies, Sig>::operator()(PyObject*, PyObject*) [with F = std::function<float(int)> (*)(const float*); Policies = boost::python::return_internal_reference<>; Sig = boost::mpl::vector2<std::function<float(int)>, const float*>; PyObject = _object]'
  /opt/local/include/boost/python/object/py_function.hpp:38:33:   required from 'PyObject* boost::python::objects::caller_py_function_impl<Caller>::operator()(PyObject*, PyObject*) [with Caller = boost::python::detail::caller<std::function<float(int)> (*)(const float*), boost::python::return_internal_reference<>, boost::mpl::vector2<std::function<float(int)>, const float*> >; PyObject = _object]'
  Test.cc:14:1:   required from here
  /opt/local/include/boost/python/detail/invoke.hpp:75:82: error: no match for call to '(const boost::python::detail::reference_existing_object_requires_a_pointer_or_reference_return_type<std::function<float(int)> >) (std::function<float(int)>)'
       return rc(f( BOOST_PP_ENUM_BINARY_PARAMS_Z(1, N, ac, () BOOST_PP_INTERCEPT) ));
                                                                                    ^
  In file included from /opt/local/include/boost/python/object/function_handle.hpp:8:0,
                   from /opt/local/include/boost/python/converter/arg_to_python.hpp:19,
                   from /opt/local/include/boost/python/call.hpp:15,
                   from /opt/local/include/boost/python/object_core.hpp:14,
                   from /opt/local/include/boost/python/args.hpp:25,
                   from /opt/local/include/boost/python.hpp:11,
                   from Test.cc:2:
  /opt/local/include/boost/python/detail/caller.hpp: In instantiation of 'static const PyTypeObject* boost::python::detail::converter_target_type<ResultConverter>::get_pytype() [with ResultConverter = boost::python::detail::reference_existing_object_requires_a_pointer_or_reference_return_type<std::function<float(int)> >; PyTypeObject = _typeobject]':
  /opt/local/include/boost/python/detail/caller.hpp:240:19:   required from 'static boost::python::detail::py_func_sig_info boost::python::detail::caller_arity<1u>::impl<F, Policies, Sig>::signature() [with F = std::function<float(int)> (*)(const float*); Policies = boost::python::return_internal_reference<>; Sig = boost::mpl::vector2<std::function<float(int)>, const float*>]'
  /opt/local/include/boost/python/object/py_function.hpp:48:35:   required from 'boost::python::detail::py_func_sig_info boost::python::objects::caller_py_function_impl<Caller>::signature() const [with Caller = boost::python::detail::caller<std::function<float(int)> (*)(const float*), boost::python::return_internal_reference<>, boost::mpl::vector2<std::function<float(int)>, const float*> >]'
  Test.cc:14:1:   required from here
  /opt/local/include/boost/python/detail/caller.hpp:102:109: error: 'struct boost::python::detail::reference_existing_object_requires_a_pointer_or_reference_return_type<std::function<float(int)> >' has no member named 'get_pytype'
           return create_result_converter((PyObject*)0, (ResultConverter *)0, (ResultConverter *)0).get_pytype();
                                                                                                               ^
  

  struct boost::python::detail:: reference_existing_object_requires_a_pointer_or_reference_return_type