C++ 自定义 class 继承本征初始化列表

Question

我正在尝试像这样从 Eigen 的向量 3 继承自定义 Vector3。

using Vector3 = Eigen::Vector3d;

enum class CustomEnum
{
    E1, E2 E3, E4,
};

class CustomVector3 : public Vector3
{
public:
    // Taken from here: https://eigen.tuxfamily.org/dox/TopicCustomizing_InheritingMatrix.html
    CustomVector3():Vector3(){}

    template<typename OtherDerived>
    CustomVector3(const Eigen::MatrixBase<OtherDerived>& other) : Vector3(other) {}

    // Initializer Constructor
    template<typename OtherDerived>
    CustomVector3(const std::initializer_list<OtherDerived>& other) : Vector3(other) {}

    template<typename OtherDerived>
    CustomVector3& operator=(const Eigen::MatrixBase<OtherDerived>& other){
        this->Vector3::operator=(other);
        return *this;
    }

    CustomEnum e = CustomEnum::E1;
};

目标是执行以下操作：

TEST_CASE("Initalizer List Test")
{
    CustomVector3 vec = {1.1, 2.2, 3.3};
    CHECK(vec.x() == 1.1);
    CHECK(vec.y() == 2.2);
    CHECK(vec.z() == 3.3);
    assert(vec.frame == CustomEnum::E1);
}

如果没有初始化构造函数，我可以执行以下操作，但不是我上面提到的目标：

Vector3 data = {1.1, 2.2, 3.3};
CustomVector3 framedData = data;

使用初始化构造函数，我得到以下编译错误消息（我在代码中将其称为 FramedVector3，但为了清楚起见，我在本文中将其称为 CustomVector3）：

/usr/include/eigen3/Eigen/src/Core/Matrix.h: In instantiation of ‘Eigen::Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols>::Matrix(const T&) [with T = std::initializer_list<double>; _Scalar = double; int _Rows = 3; int _Cols = 1; int _Options = 0; int _MaxRows = 3; int _MaxCols = 1]’:
/home/seedship/uavAP/include/uavAP/Core/FramedVector3.h:23:81:   required from ‘FramedVector3::FramedVector3(const std::initializer_list<_Tp>&) [with OtherDerived = double]’
/home/seedship/uavAP/include/uavAP/Core/SensorData.h:128:38:   required from here
/usr/include/eigen3/Eigen/src/Core/Matrix.h:294:31: error: no matching function for call to ‘Eigen::Matrix<double, 3, 1>::_init1<std::initializer_list<double> >(const std::initializer_list<double>&)’
  294 |       Base::template _init1<T>(x);
      |       ~~~~~~~~~~~~~~~~~~~~~~~~^~~
In file included from /usr/include/eigen3/Eigen/Core:462,
                 from /usr/include/eigen3/Eigen/Dense:1,
                 from /usr/local/include/cpsCore/Utilities/LinearAlgebra.h:13,
                 from /home/seedship/uavAP/include/uavAP/Core/FramedVector3.h:9,
                 from /home/seedship/uavAP/include/uavAP/Core/SensorData.h:11,
                 from /home/seedship/uavAP/include/uavAP/Core/Orientation/ENU.h:8,
                 from /home/seedship/uavAP/src/Core/Orientation/ENU.cpp:5:
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h:774:30: note: candidate: ‘void Eigen::PlainObjectBase<Derived>::_init1(Eigen::Index, typename Eigen::internal::enable_if<(((typename Eigen::internal::dense_xpr_base<Derived>::type::SizeAtCompileTime != 1) || (! Eigen::internal::is_convertible<T, typename Eigen::internal::traits<T>::Scalar>::value)) && ((! Eigen::internal::is_same<typename Eigen::internal::traits<T>::XprKind, Eigen::ArrayXpr>::value) || (typename Eigen::internal::dense_xpr_base<Derived>::type::SizeAtCompileTime == Eigen::Dynamic))), T>::type*) [with T = std::initializer_list<double>; Derived = Eigen::Matrix<double, 3, 1>; Eigen::Index = long int; typename Eigen::internal::enable_if<(((typename Eigen::internal::dense_xpr_base<Derived>::type::SizeAtCompileTime != 1) || (! Eigen::internal::is_convertible<T, typename Eigen::internal::traits<T>::Scalar>::value)) && ((! Eigen::internal::is_same<typename Eigen::internal::traits<T>::XprKind, Eigen::ArrayXpr>::value) || (typename Eigen::internal::dense_xpr_base<Derived>::type::SizeAtCompileTime == Eigen::Dynamic))), T>::type = std::initializer_list<double>]’
  774 |     EIGEN_STRONG_INLINE void _init1(Index size, typename internal::enable_if<    (Base::SizeAtCompileTime!=1 || !internal::is_convertible<T, Scalar>::value)
      |                              ^~~~~~
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h:774:43: note:   no known conversion for argument 1 from ‘const std::initializer_list<double>’ to ‘Eigen::Index’ {aka ‘long int’}
  774 |     EIGEN_STRONG_INLINE void _init1(Index size, typename internal::enable_if<    (Base::SizeAtCompileTime!=1 || !internal::is_convertible<T, Scalar>::value)
      |                                     ~~~~~~^~~~
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h:788:30: note: candidate: ‘template<class T> void Eigen::PlainObjectBase<Derived>::_init1(const Scalar&, typename Eigen::internal::enable_if<((typename Eigen::internal::dense_xpr_base<Derived>::type::SizeAtCompileTime == 1) && Eigen::internal::is_convertible<T, typename Eigen::internal::traits<T>::Scalar>::value), T>::type*) [with T = T; Derived = Eigen::Matrix<double, 3, 1>]’
  788 |     EIGEN_STRONG_INLINE void _init1(const Scalar& val0, typename internal::enable_if<Base::SizeAtCompileTime==1 && internal::is_convertible<T, Scalar>::value,T>::type* = 0)
      |                              ^~~~~~
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h:788:30: note:   template argument deduction/substitution failed:
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h: In substitution of ‘template<class T> void Eigen::PlainObjectBase<Eigen::Matrix<double, 3, 1> >::_init1<T>(const Scalar&, typename Eigen::internal::enable_if<((Eigen::MatrixBase<Eigen::Matrix<double, 3, 1> >::SizeAtCompileTime == 1) && Eigen::internal::is_convertible<T, double>::value), T>::type*) [with T = std::initializer_list<double>]’:
/usr/include/eigen3/Eigen/src/Core/Matrix.h:294:31:   required from ‘Eigen::Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols>::Matrix(const T&) [with T = std::initializer_list<double>; _Scalar = double; int _Rows = 3; int _Cols = 1; int _Options = 0; int _MaxRows = 3; int _MaxCols = 1]’
/home/seedship/uavAP/include/uavAP/Core/FramedVector3.h:23:81:   required from ‘FramedVector3::FramedVector3(const std::initializer_list<_Tp>&) [with OtherDerived = double]’
/home/seedship/uavAP/include/uavAP/Core/SensorData.h:128:38:   required from here
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h:788:30: error: invalid use of incomplete type ‘struct Eigen::internal::enable_if<false, std::initializer_list<double> >’
[Truncated for brevity]

谁能解释我错过了什么？ 我很困惑为什么赋值运算符有效，而不是构造函数。 这发生在 Eigen 3.3.9-1 和 eigen-git 上。

更新：也许这个问题是非常特定于库的，所以我在 Eigen gitlab 项目（ https://gitlab.com/libeigen/eigen/-/issues/2192 ）上询问

Answer 1

您需要使用一对额外的括号。 模板化这个构造函数也没有意义，因为模板参数类型需要匹配特征向量的标量类型，如果您希望标量类型可配置，您需要模板化整个 class。

总之

CustomVector3(const std::initializer_list<double>& other) : Vector3({other}) {}

是这样做的正确方法。 原因是Eigen::Vector3d是Eigen::Matrix<double, 3, 1>的 typedef。 然而，矩阵的初始化列表构造函数需要处理多行和多列，因此具有签名

explicit PlainObjectBase(const std::initializer_list<std::initializer_list<Scalar>>& list);

如果您总是想使用 3D 向量，（更简单的）替代方法是使用 Eigen 的 3D 构造函数和聚合初始化：

CustomVector3(double x, double y, double z) : Vector3(x, y, z) {}