No known expression from value to value&… Why?

Question

I have tried writing a function which takes a ColXpr value as input:

typedef Eigen::Array Signal2D;

vo         


        

Answer 1

In C++, a temporary object cannot bind to a non-const reference.

I'm assuming that arr.col(0) returns an object by value. The returned value is a temporary object. This means it cannot match a parameter of type T &.

One solution:

auto temp = arr.col(0);
Threshold(temp);

I wonder if you intended for arr.col() to return a reference?