Avoiding ambiguous parameters in templated Eigen functions with MSVS - c++

Question

I'm writing some funtions that are supposed to take Eigen::Array as an input.
The Arrays are of constant size, but the size is a template parameter and should be deducted from the input.
When compiling with MSVS, i have to supply the size to the function or it will result in an error.
#include <Eigen/Core>
template<unsigned short t_iSize>
void foo(const Eigen::Array<unsigned short, t_iSize, 1>&)
{
}
int main()
{
Eigen::Array<unsigned short, 3, 1> test;
// foo(test); // Compiler errors C2672 and C2784
foo<3>(test); // Giving the size solves the errors
}
The size should be possible to be deducted from the variable test, but it seems to fail when computing the template arguments 4 and 5 for the Array.
Error C2672: "foo": no matching overloaded function found.
Error C2784: "void foo(const Eigen::Array< unsigned short,t_iSize,1,|_Rows==&&?:&&_Rows!=?:,_Rows,1> &)": could not deduce template argument for "const Eigen::Array< unsigned short,t_iSize,1,|_Rows==&&?:&&_Rows!=?:,_Rows,1> &" from "Eigen::Array< unsigned short,3,1,0,3,1>".
Is it possible to avoid this problem when taking the Eigen::Array, or do I need to take Eigen::ArrayBase as a function parameter? I would like to avoid that, as it obscures the fact that the function only takes this specific type of arrays.
Edit:
As Jarod42 noted, the template parameter should be of type int.
Visual Studio can compile the code with this mistake.
It fails in deducing the parameter _Rows, though, where other compilers can do so.
Here you can see the problem I ran into.

Answer 1

Declaration of Eigen::Array is
template<typename _Scalar, int _Rows, int _Cols, int _Options, int _MaxRows, int _MaxCols>
class Eigen::Array;
Your function uses wrong type for row, unsigned short should be int.
template <int t_iSize>
void foo(const Eigen::Array<unsigned short, t_iSize, 1>&)
{
// ...
}
Demo
As workaround for your issue with Msvc, you might do:
apply the default value manually:
template <int t_iSize>
void bar(const Eigen::Array<unsigned short, t_iSize, 1, 0, t_iSize, 1>&) {
// ...
}
or add the extra template (and so the code is even more generic):
template <int t_iSize, int Options, int MaxRows, int MaxCols>
void foo(const Eigen::Array<unsigned short, t_iSize, 1, Options, MaxRows, MaxCols>&) {
// ...
}
Demo