CODEWITHSUNDEEP
c++eigeneigen3
red-patriot
red-patriot

Reputation: 23

C++ Function Template is not deducing Eigen vector sizes

I have written a function

template <int N>
bool checkColinear(const std::array<Eigen::Vector<double, N>, 3>& points) noexcept;

which takes three N-D points and returns true if they are collinear within a certain tolerance. Everything works if I call the function and explicitly specify N:

std::array<Eigen::Vector3d, 3> points = {Eigen::Vector3d{0.0, 1.0, 0.0},
                                         Eigen::Vector3d{0.0, 3.0, 0.0},
                                         Eigen::Vector3d{0.0, 2.0, 0.0}};

auto result = checkCollinear<3>(points);

But if I try to call the function without specifying N explicitly the compiler reports an error:

auto result = checkCollinear(points);

The error I get is "error C2672: 'checkCollinear': no matching overloaded function found". Is it possible for the compiler to deduce the template argument in this case? I am using MSVC143 (VS2022) and using C++20.

I have already tried to explicitly change the Eigen::Vector3d to Eigen::Vector<double, 3> and Eigen::Matrix<double, 3, 1>, but that neither of those fix it. I have also tried making the type of N a std::size_t too, but that doesn't help either.

Upvotes: 2

Views: 253

Answers (1)

Ranoiaetep
Ranoiaetep

Reputation: 6637

As mentioned in the comments, this is likely a bug. A workaround is to spell out the full type name for Vector<double, N> as:

Matrix<double, N,  1,          0,            N,         1>
                   ^           ^             ^          ^
                  col    row/col major    max rol    max col

And your function signature will become:

template <int N>
bool checkCollinear(const std::array<Eigen::Matrix<double, N, 1, 0, N, 1>, 3>& points) noexcept;

Demo

Upvotes: 2

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