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| #include <iostream> | |
| #include <Eigen/Dense> | |
| #include <concepts> | |
| namespace Eigen { | |
| template <int D, typename Derived> | |
| inline auto& get(Eigen::DenseCoeffsBase<Derived, WriteAccessors>& p) { return p.coeffRef(D); } | |
| template <int D, typename Derived> | |
| inline const auto get(const Eigen::DenseCoeffsBase<Derived,ReadOnlyAccessors>& p) { return p.coeff(D); } | |
| template <typename Derived> | |
| concept StaticSizePlainObjectBase = std::derived_from<Derived,Eigen::PlainObjectBase<Derived>> && | |
| (Derived::RowsAtCompileTime >0 && Derived::ColsAtCompileTime > 0); | |
| template <typename Derived> | |
| concept StaticSizeEigenBase = std::derived_from<Derived,Eigen::EigenBase<Derived>> && | |
| (Derived::RowsAtCompileTime >0 && Derived::ColsAtCompileTime > 0); | |
| } | |
| namespace std { | |
| template <typename Derived> requires Eigen::StaticSizeEigenBase<Derived> | |
| struct tuple_size<Derived> { | |
| constexpr static int value = Derived::RowsAtCompileTime * Derived::ColsAtCompileTime; | |
| }; | |
| template <size_t D, typename Derived> requires Eigen::StaticSizeEigenBase<Derived> && | |
| (D < Derived::RowsAtCompileTime * Derived::ColsAtCompileTime) | |
| struct tuple_element<D,Derived> { | |
| using type = typename Derived::Scalar; | |
| }; | |
| } | |
| int main(int argc, char * argv[]) { | |
| // We can use a structured binding to populate an eigen vector! | |
| Eigen::Vector3d p; | |
| auto& [x,y,z] = p; | |
| x = 2; | |
| y = 3; | |
| z = 4; | |
| // works for Array, const, int, and size 2! | |
| const Eigen::Array2i q = p.head<2>().cast<int>().array(); | |
| auto& [u,v] = q; | |
| // even works on expression templates! | |
| auto [u2,v2] = 2*q; | |
| std::cout << p.transpose() << std::endl; | |
| std::cout << u << "," << v << std::endl; | |
| std::cout << u2 << "," << v2 << std::endl; | |
| // Can use to read blocks, but not write... yet! | |
| Eigen::Matrix3f A; | |
| A.setIdentity(); | |
| auto [m,n,o] = A.col(2); | |
| std::cout << m << "," << n << "," << o << std::endl; | |
| } |
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