This code is well formed and successfully compiled, but cannot be linked.

<pre><code class="cpp">

<pre>
#include <opencv2/opencv.hpp>

int main(int argc, char* argv[])
{
cv::Mat_<uint8_t> img(128, 128);
cv::Mat img2 = img.clone();;

img.operator()(cv::Vec2i(0,0));
img2.at<uint8_t>(cv::Vec2i(0,0));

return 0;
}
</code></pre> </pre>

cause @cv::Mat::at<typename>(cv::Vec<int,n>)@ cv::Mat::at<typename>(cv::Vec<int,n>) is defined but not implemented on core.hpp.

I think we should remove its definition or write its implementation.