c++ - 具有自定义标量类型的特征:具有自定义类型的矩阵乘法因 `use of overloaded operator '而失败*' is ambiguous`

Question

我正在尝试在official documentation之后将boost.units集成到Eigen中。我也查看了两个执行相同操作的项目，并且我也用它们的代码测试了该操作，尽管我遇到了相同的错误(Project 1 Project 2)。

我遇到的问题是，在将两个矩阵与基于boost::units的自定义标量类型相乘时，乘法运算符似乎存在一些歧义。
clang 10.0.0.3和Apple clang 11.0.3会发生此行为。

触发错误的代码(use of overloaded operator '*' is ambiguous)如下:

    const Eigen::Matrix<boost::units::quantity<boost::units::si::length, double>, 2, 3> x;
    const Eigen::Matrix<boost::units::quantity<boost::units::si::dimensionless, double>, 3, 1> y;
    const Eigen::Matrix<boost::units::quantity<boost::units::si::length, double>, 2, 1> result = x * y;

对于集成，我创建了包含 NumTraits的 boost::units::quantity<T>的文件，如下所示:

namespace Eigen {

template<class T> struct NumTraits<boost::units::quantity<T>> : NumTraits<double> {
    typedef boost::units::quantity<T> Real;
    typedef boost::units::quantity<T> NonInteger;
    typedef boost::units::quantity<T> Nested;

    enum {
        IsComplex             = 0,
        IsInteger             = 0,
        IsSigned              = 1,
        RequireInitialization = 1,
        ReadCost              = 1,
        AddCost               = 3,
        MulCost               = 3
    };
};
} // namespace Eigen

对于乘法支持，我具有以下 struct定义:

namespace Eigen {

namespace units = boost::units;

template<typename scalarA, typename scalarB>
struct ScalarBinaryOpTraits<units::quantity<scalarA>, scalarB,
    internal::scalar_product_op<units::quantity<scalarA>, scalarB>> {
    typedef units::quantity<typename units::multiply_typeof_helper<scalarA, scalarB>::type> ReturnType;
};

template<typename scalarA, typename scalarB>
struct ScalarBinaryOpTraits<scalarA, units::quantity<scalarB>,
    internal::scalar_product_op<scalarA, units::quantity<scalarB>>> {
    typedef units::quantity<typename units::multiply_typeof_helper<scalarA, scalarB>::type> ReturnType;
};

template<typename scalarA, typename scalarB>
struct ScalarBinaryOpTraits<scalarA, units::quantity<scalarB>,
    internal::scalar_product_op<units::quantity<scalarA>, units::quantity<scalarB>>> {
    typedef units::quantity<typename units::multiply_typeof_helper<scalarA, scalarB>::type> ReturnType;
};

template<typename scalarA, typename scalarB>
struct ScalarBinaryOpTraits<units::quantity<scalarA>, scalarB,
    internal::scalar_conj_product_op<units::quantity<scalarA>, scalarB>> {
    typedef typename units::multiply_typeof_helper<scalarA, scalarB>::type ReturnType;
};

template<typename scalarA, typename scalarB>
struct ScalarBinaryOpTraits<scalarA, units::quantity<scalarB>,
    internal::scalar_conj_product_op<scalarA, units::quantity<scalarB>>> {
    typedef typename units::multiply_typeof_helper<scalarA, scalarB>::type ReturnType;
};

template<typename scalarA, typename scalarB>
struct ScalarBinaryOpTraits<units::quantity<scalarA>, units::quantity<scalarB>,
    internal::scalar_conj_product_op<units::quantity<scalarA>, units::quantity<scalarB>>> {
    typedef units::quantity<typename units::multiply_typeof_helper<scalarA, scalarB>::type> ReturnType;
};

} // namespace Eigen

完整的错误输出:

Scanning dependencies of target LaserCalibration
[  8%] Building CXX object CMakeFiles/LaserCalibration.dir/maths/Maths.cpp.o
/Users/dwright/projects/dv-laser-calibration/maths/Maths.cpp:9:97: error: use of overloaded operator '*' is ambiguous (with operand types 'const Eigen::Matrix<boost::units::quantity<boost::units::si::length, double>, 2, 3>' (aka 'const Matrix<quantity<unit<list<dim<boost::units::length_base_dimension, static_rational<1> >, boost::units::dimensionless_type>, homogeneous_system<list<boost::units::si::meter_base_unit, boost::units::list<boost::units::scaled_base_unit<boost::units::cgs::gram_base_unit, boost::units::scale<10, static_rational<3> > >, boost::units::list<boost::units::si::second_base_unit, boost::units::list<boost::units::si::ampere_base_unit, boost::units::list<boost::units::si::kelvin_base_unit, boost::units::list<boost::units::si::mole_base_unit, boost::units::list<boost::units::si::candela_base_unit, boost::units::list<boost::units::angle::radian_base_unit, boost::units::list<boost::units::angle::steradian_base_unit, boost::units::dimensionless_type> > > > > > > > > > >, double>, 2, 3>') and 'const Eigen::Matrix<boost::units::quantity<boost::units::si::dimensionless, double>, 3, 1>' (aka 'const Matrix<quantity<unit<boost::units::dimensionless_type, homogeneous_system<list<boost::units::si::meter_base_unit, boost::units::list<boost::units::scaled_base_unit<boost::units::cgs::gram_base_unit, boost::units::scale<10, static_rational<3> > >, boost::units::list<boost::units::si::second_base_unit, boost::units::list<boost::units::si::ampere_base_unit, boost::units::list<boost::units::si::kelvin_base_unit, boost::units::list<boost::units::si::mole_base_unit, boost::units::list<boost::units::si::candela_base_unit, boost::units::list<boost::units::angle::radian_base_unit, boost::units::list<boost::units::angle::steradian_base_unit, boost::units::dimensionless_type> > > > > > > > > > >, double>, 3, 1>'))
        const Eigen::Matrix<boost::units::quantity<boost::units::si::length, double>, 2, 1> result = x * y;
                                                                                                     ~ ^ ~
/usr/local/include/eigen3/Eigen/src/Core/../plugins/CommonCwiseBinaryOps.h:50:29: note: candidate function [with T = Eigen::Matrix<boost::units::quantity<boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension, boost::units::static_rational<1, 1> >, boost::units::dimensionless_type>, boost::units::homogeneous_system<boost::units::list<boost::units::si::meter_base_unit, boost::units::list<boost::units::scaled_base_unit<boost::units::cgs::gram_base_unit, boost::units::scale<10, static_rational<3> > >, boost::units::list<boost::units::si::second_base_unit, boost::units::list<boost::units::si::ampere_base_unit, boost::units::list<boost::units::si::kelvin_base_unit, boost::units::list<boost::units::si::mole_base_unit, boost::units::list<boost::units::si::candela_base_unit, boost::units::list<boost::units::angle::radian_base_unit, boost::units::list<boost::units::angle::steradian_base_unit, boost::units::dimensionless_type> > > > > > > > > >, void>, double>, 2, 3, 0, 2, 3>]
EIGEN_MAKE_SCALAR_BINARY_OP(operator*,product)
                            ^
/usr/local/include/eigen3/Eigen/src/Core/../plugins/CommonCwiseBinaryOps.h:50:29: note: candidate function [with T = Eigen::Matrix<boost::units::quantity<boost::units::unit<boost::units::dimensionless_type, boost::units::homogeneous_system<boost::units::list<boost::units::si::meter_base_unit, boost::units::list<boost::units::scaled_base_unit<boost::units::cgs::gram_base_unit, boost::units::scale<10, static_rational<3> > >, boost::units::list<boost::units::si::second_base_unit, boost::units::list<boost::units::si::ampere_base_unit, boost::units::list<boost::units::si::kelvin_base_unit, boost::units::list<boost::units::si::mole_base_unit, boost::units::list<boost::units::si::candela_base_unit, boost::units::list<boost::units::angle::radian_base_unit, boost::units::list<boost::units::angle::steradian_base_unit, boost::units::dimensionless_type> > > > > > > > > >, void>, double>, 3, 1, 0, 3, 1>]
/usr/local/include/eigen3/Eigen/src/Core/MatrixBase.h:166:5: note: candidate function [with OtherDerived = Eigen::Matrix<boost::units::quantity<boost::units::unit<boost::units::dimensionless_type, boost::units::homogeneous_system<boost::units::list<boost::units::si::meter_base_unit, boost::units::list<boost::units::scaled_base_unit<boost::units::cgs::gram_base_unit, boost::units::scale<10, static_rational<3> > >, boost::units::list<boost::units::si::second_base_unit, boost::units::list<boost::units::si::ampere_base_unit, boost::units::list<boost::units::si::kelvin_base_unit, boost::units::list<boost::units::si::mole_base_unit, boost::units::list<boost::units::si::candela_base_unit, boost::units::list<boost::units::angle::radian_base_unit, boost::units::list<boost::units::angle::steradian_base_unit, boost::units::dimensionless_type> > > > > > > > > >, void>, double>, 3, 1, 0, 3, 1>]
    operator*(const MatrixBase<OtherDerived> &other) const;
    ^
/Users/dwright/projects/dv-laser-calibration/maths/Maths.cpp:6:106: warning: unused parameter 'event' [-Wunused-parameter]
Eigen::Matrix<boost::units::quantity<double>, 2, 1> Maths::convertToPhysicalCoordinates(const dv::Event &event) const {
                                                                                                         ^
In file included from /Users/dwright/projects/dv-laser-calibration/maths/Maths.cpp:1:
/Users/dwright/projects/dv-laser-calibration/maths/Maths.hpp:16:25: warning: private field 'parameters' is not used [-Wunused-private-field]
        CalibrationParameters &parameters;
                               ^
2 warnings and 1 error generated.
make[2]: *** [CMakeFiles/LaserCalibration.dir/maths/Maths.cpp.o] Error 1
make[1]: *** [CMakeFiles/LaserCalibration.dir/all] Error 2
make: *** [all] Error 2
11:04:41: The process "/usr/local/Cellar/cmake/3.17.2/bin/cmake" exited with code 2.
Error while building/deploying project LaserCalibration (kit: Imported Kit)
When executing step "CMake Build"
11:04:41: Elapsed time: 00:02.

Answer 1

忽略共轭乘积特征，我可以看到第三个特化似乎已经消失了:

template <typename scalarA, typename scalarB>
    struct ScalarBinaryOpTraits<
    scalarA, units::quantity<scalarB>,
    internal::scalar_product_op<units::quantity<scalarA>,
    units::quantity<scalarB>>> {
        typedef units::quantity<
            typename units::multiply_typeof_helper<scalarA, scalarB>::type>
            ReturnType;
    };

该行:

    scalarA, units::quantity<scalarB>,

应该阅读:

    units::quantity<scalarA>, units::quantity<scalarB>,

消除原因

我们刚刚确定的第三个专业显然应该与我们的情况相匹配。但是，其他专长不排除两个标量都是数量的情况。

注释掉不相关的两个确实使事情顺利了:

Live On Compiler Explorer

#include <boost/units/unit.hpp>
#include <boost/units/io.hpp>
#include <boost/units/limits.hpp>
#include <boost/units/quantity.hpp>
#include <boost/units/systems/si.hpp>
#include <boost/units/cmath.hpp>
#include <Eigen/Core>

namespace Eigen {
    namespace units = boost::units;

#if 0
    template <typename scalarA, typename scalarB>
        struct ScalarBinaryOpTraits<
        units::quantity<scalarA>, scalarB,
        internal::scalar_product_op<units::quantity<scalarA>, scalarB>> {
            typedef units::quantity<
                typename units::multiply_typeof_helper<scalarA, scalarB>::type>
                ReturnType;
        };
#endif

#if 0
    template <typename scalarA, typename scalarB>
        struct ScalarBinaryOpTraits<
        scalarA, units::quantity<scalarB>,
        internal::scalar_product_op<scalarA, units::quantity<scalarB>>> {
            typedef units::quantity<
                typename units::multiply_typeof_helper<scalarA, scalarB>::type>
                ReturnType;
        };
#endif

#if 1
    template <typename scalarA, typename scalarB>
        struct ScalarBinaryOpTraits<
        units::quantity<scalarA>, units::quantity<scalarB>,
        internal::scalar_product_op<units::quantity<scalarA>,
        units::quantity<scalarB>>> {
            typedef units::quantity<
                typename units::multiply_typeof_helper<scalarA, scalarB>::type>
                ReturnType;
        };
#endif
} // namespace Eigen

#include <iostream>
int main() {
    using V = boost::units::quantity<boost::units::si::length, double>;
    using U = boost::units::quantity<boost::units::si::dimensionless, double>;
    constexpr auto Vu = boost::units::si::meter;
    constexpr auto Uu = 1.0;

    Eigen::Matrix<V, 2, 3> x;
    Eigen::Matrix<U, 3, 1> y;

    x << 1*Vu, 2*Vu, 3*Vu, 4*Vu, 5*Vu, 6*Vu;
    y << 1*Uu, 2*Uu, 3*Uu;

    std::cout << "x:\n" << x << "\n";
    std::cout << "y:\n" << y << "\n";
    auto result = (x * y).eval();

    std::cout << "result:\n" << result << "\n";
}

版画

x:
  1 m   2 m   3 m
  4 m   5 m   6 m
y:
              1 dimensionless
              2 dimensionless
              3 dimensionless
result:
  14 m
  32 m

固定？

我会尝试将所有三个结合在一起。但是 ScalarBinaryOpTraits不支持SFINAE。尽管如此，我还是试图让事情变得顺利:

namespace Eigen {
    namespace units = boost::units;

    namespace /*file-static*/ {
        template <typename A, typename B, typename R = units::multiply_typeof_helper<A, B> >
        struct QuantityProductImpl {
            using ReturnType = typename R::type;
        };
    }

    template <typename A, typename B>
        struct ScalarBinaryOpTraits<A, B,
            std::enable_if_t< units::is_quantity<A>::value && units::is_quantity<B>::value,
                internal::scalar_product_op<A, B>
            >
        > : QuantityProductImpl<A, B> { };
} // namespace Eigen

哪个确实像以前一样工作: Live On Compiler Explorer

但是，如果将 &&更改为 ||(或XOR逻辑的 !=)，我们将再次变得模棱两可。不知道如何进行，但是也许可以给您一些想法？