C++ Custom class inhereting Eigen initializer list - c++

Question

I am trying to make a custom Vector3 inheriting from Eigen's vector 3 like so.
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;
};
And the goal is to do the following:
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);
}
Without the initializer constructor, I am able to do the following, but not my goal mentioned above:
Vector3 data = {1.1, 2.2, 3.3};
CustomVector3 framedData = data;
With the initializer constructor, I get the following compile error message (I called it FramedVector3 in my code, but for clarity I called it CustomVector3 in this post):
/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]
Can anyone explain what I am missing? I'm confused why the assignment operator works, but not the constructor. This happens on both Eigen 3.3.9-1 and eigen-git.
Update: maybe this question is very library specific, so I asked on the Eigen gitlab project (https://gitlab.com/libeigen/eigen/-/issues/2192)

Answer 1

You need to use an extra pair of parenthesis. Also there is no point in templating this constructor since the template argument type needs to match the scalar type of the Eigen vector and if you'd like the scalar type to be configurable you'd need to template the whole class.
In summary
CustomVector3(const std::initializer_list<double>& other) : Vector3({other}) {}
is the correct way to do this. The reason is that Eigen::Vector3d is a typedef for Eigen::Matrix<double, 3, 1>. The initializer list constructor for matrices needs to handle multiple rows and columns however and has thus the signature
explicit PlainObjectBase(const std::initializer_list<std::initializer_list<Scalar>>& list);
If you always want to use 3D vectors the (easier) alternative is to use Eigen's 3D constructor and aggregate initialization:
CustomVector3(double x, double y, double z) : Vector3(x, y, z) {}