[eigen] Tensor .select() with mixed tensor/scalar arguments

[Wood, Tobias]

Hello,

The following simplified program does not compile with Eigen HEAD:

#include <unsupported/Eigen/CXX11/Tensor>

int main(const int argc, const char *const argv[])
{
  Eigen::Tensor<float, 2> ft_A(2, 4), ft_B(2, 4), ft_result(2, 4);
  ft_A.setRandom();
  ft_B.setZero();
  ft_result = (ft_A < 0.5f).select(ft_A, ft_B);
  ft_result = (ft_A < 0.5f).select(ft_A, 0.f);
}

The first call to ft_result compiles fine, but the second does not. The first 
line of compile errors is:

Eigen/src/Core/util/ForwardDeclarations.h:23:47: error: implicit instantiation 
of undefined template 'Eigen::internal::traits<float>

So it looks to me like Eigen tries to treat the 0.f as an Eigen tensor, rather 
than as the scalar type.

Does this count as a bug and if so should I open a bug on the tracker? I looked 
at trying to fix it myself but sadly this kind of Eigen issue is out of my 
league.

Best wishes,
Toby