如何使用 C++20 模块包装实现？

问题描述

我在包装可比较距离的增强几何实现时遇到问题。我不确定是因为我使用的模块不正确还是 boost 几何本身有问题。 在我的模块文件中：

module;

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/register/point.hpp>

export module module_interface;
export import "point.hpp"; // Defines MyPoint as a plain struct with members float x,y; 
export {
    BOOST_GEOMETRY_REGISTER_POINT_2D(MyPoint,float,cs::cartesian,x,y)
};

namespace m3 {
    export template <typename A>
        auto MyFunc(A& a,A& b) {
        return boost::geometry::comparable_distance(a,b);
    }

    export auto MyFunc2() {
        MyPoint a{ 0,0 },b{ 1,1 };
        return MyFunc(a,b);
    }
};

在调用程序中我有：

#include <iostream>
import module_interface;

using namespace m3;

int main() {

    MyPoint a{ 0,1 };
        
    auto t = m3::MyFunc(a,b); // I want to do this,but it does not compile
    auto t1 = m3::MyFunc2(); // this does compiles and may help isolate problem
}

当我编译时，我得到一个冗长的错误（我觉得这没有帮助，但也许对你有帮助）

> include\boost\geometry\strategies\cartesian\distance_pythagoras.hpp(235,1):
> error C3967: error importing 'type' from module 'module_interface'
> include\boost\geometry\strategies\comparable_distance_result.hpp(48):
> message : see reference to class template instantiation
> 'boost::geometry::strategy::distance::services::return_type<boost::geometry::strategy::distance::comparable::pythagoras<CalculationType>,MyPoint,MyPoint>'
> being compiled 1>        with 1>        [ 1>           
> CalculationType=void 1>        ]
> include\boost\geometry\strategies\comparable_distance_result.hpp(61):
> message : see reference to class template instantiation
> 'boost::geometry::resolve_strategy::comparable_distance_result<Geometry1,Geometry2,boost::geometry::strategy::distance::services::default_strategy<boost::geometry::point_tag,boost::geometry::point_tag,boost::geometry::cartesian_tag,void>::type,true>'
> being compiled 1>        with 1>        [ 1>           
> Geometry1=MyPoint,1>            Geometry2=MyPoint 1>        ]
> include\boost\geometry\strategies\comparable_distance_result.hpp(132):
> message : see reference to class template instantiation
> 'boost::geometry::resolve_strategy::comparable_distance_result<Geometry1,Strategy,1>            Geometry2=MyPoint,1>           
> Strategy=boost::geometry::default_strategy 1>        ]
include\boost\geometry\strategies\comparable_distance_result.hpp(243):
> message : see reference to class template instantiation
> 'boost::geometry::resolve_variant::comparable_distance_result<Geometry1,Strategy>'
> being compiled 1>        with 1>        [ 1>           
> Geometry1=MyPoint,1>           
> Strategy=boost::geometry::default_strategy 1>        ]
include\boost\geometry\strategies\comparable_distance_result.hpp(248):
> message : see reference to class template instantiation
> 'boost::geometry::comparable_distance_result<Geometry1,boost::geometry::default_strategy>'
> being compiled 1>        with 1>        [ 1>           
> Geometry1=MyPoint,1>            Geometry2=MyPoint 1>        ]
> include\boost\geometry\strategies\default_comparable_distance_result.hpp(37):
> message : see reference to class template instantiation
> 'boost::geometry::comparable_distance_result<Geometry1,void>'
> being compiled 1>        with 1>        [ 1>           
> Geometry1=MyPoint,1>            Geometry2=MyPoint 1>        ]
> 1>test_modules\module_interface\module_interface.ixx(15):
> message : see reference to class template instantiation
> 'boost::geometry::default_comparable_distance_result<A,A>' being
> compiled 1>        with 1>        [ 1>            A=MyPoint 1>       
> ]
> 1>include\boost\geometry\algorithms\detail\comparable_distance\interface.hpp(358):
> message : see reference to function template instantiation
> 'default_comparable_distance_result<Geometry1,Geometry2>::type
> boost::geometry::comparable_distance(const Geometry1 &,const Geometry2
> &)' being compiled
> 1>test_modules\module_consumer\consumer.cpp(10):
> message : see reference to function template instantiation 'auto
> m3::MyFunc<MyPoint>(A &,A &)' being compiled 1>        with 1>       
> [ 1>            A=MyPoint 1>        ]

解决方法

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