CODEWITHSUNDEEP
c++enumseigen
Emanuele Paolini
Emanuele Paolini

Reputation: 10162

c++ eigen static assert confuses enum with float

Here is the code:

#include <Eigen/Dense>
using namespace Eigen;
enum { TWO = 2};
Matrix<float, Dynamic, TWO> m1(42, 2); // good...
Matrix<float, Dynamic, TWO> m2(42, int(TWO)); // good...
Matrix<float, Dynamic, TWO> m3(42, TWO); // error!

When I compile the declaration of m3 is raising an error as if the enum value TWO is a floating point number:

$ g++ -I/usr/include/eigen3 -c bug.cpp
In file included from /usr/include/eigen3/Eigen/Core:366,
                 from /usr/include/eigen3/Eigen/Dense:1,
                 from bug.cpp:1:
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h: In instantiation of ‘void Eigen::PlainObjectBase<Derived>::_init2(Eigen::Index, Eigen::Index, typename Eigen::internal::enable_if<(typename Eigen::internal::dense_xpr_base<Derived>::type::SizeAtCompileTime != 2), T0>::type*) [with T0 = int; T1 = <unnamed enum>; Derived = Eigen::Matrix<float, -1, 2>; Eigen::Index = long int; typename Eigen::internal::enable_if<(typename Eigen::internal::dense_xpr_base<Derived>::type::SizeAtCompileTime != 2), T0>::type = int]’:
/usr/include/eigen3/Eigen/src/Core/Matrix.h:302:35:   required from ‘Eigen::Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols>::Matrix(const T0&, const T1&) [with T0 = int; T1 = <unnamed enum>; _Scalar = float; int _Rows = -1; int _Cols = 2; int _Options = 0; int _MaxRows = -1; int _MaxCols = 2]’
bug.cpp:6:39:   required from here
/usr/include/eigen3/Eigen/src/Core/PlainObjectBase.h:740:58: error: static assertion failed: FLOATING_POINT_ARGUMENT_PASSED__INTEGER_WAS_EXPECTED
  740 |       EIGEN_STATIC_ASSERT(bool(NumTraits<T0>::IsInteger) &&
      |                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
  741 |                           bool(NumTraits<T1>::IsInteger),
      |                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
/usr/include/eigen3/Eigen/src/Core/util/StaticAssert.h:33:54: note: in definition of macro ‘EIGEN_STATIC_ASSERT’
   33 |     #define EIGEN_STATIC_ASSERT(X,MSG) static_assert(X,#MSG);
      |

Upvotes: 1

Views: 210

Answers (1)

user17732522
user17732522

Reputation: 76658

The error message is just not chosen well since it always mentions floating points as causing the issue, but the point is that you need to pass an integer type, which an enumeration type is not.

However, with Eigen version 3.3.8 this has been changed and an enumeration type is now accepted as well and will be converted to its underlying integer type, see this issue resulting in this commit. Since that version your code compiles fine, see https://godbolt.org/z/W4jYbKfns.

Upvotes: 5

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