C＆＃x2B;＆＃x2B; eigen静态断言使枚举与浮子混淆

Question

这是代码：

#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!

当我编译时，M3的声明会引起错误，好像枚举值两个是浮点数：

$ 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);
      |                       

Answer 1

错误消息只是选择不正确，因为它总是将浮点提及引起问题，但要点是您需要通过整数类型，而枚举类型不是。

但是，使用EIGEN版本3.3.8，这已更改，现在也接受了枚举类型，并将转换为其基础整数类型，请参见此问题导致 。由于该版本您的代码填充了，因此请参见 https://godbolt.org/z/w4jybkfns 。