Passing a functor into a templated function

Question

I am new to templating, but I am trying to make my primms algorithm work with two different distance calculators(thats what the functors are for) based on different constraints for a school project (they calculate the distance differently, one depends on if we care about terrain and the other does not). I declare like this

template <typename func>
    double mst_mode(std::vector<primms_vertex> &mst_vec, const func &comp){

But later in the function when I attempt to use it like this:

if(i != working_vertex && !mst_vec[i].been_visited && mst_vec[i].distance > comp(mst_vec[working_vertex], mst_vec[i])){

I get the following errors :

No matching function for call to object of type 'const primms_vertex::euclids_distance' No matching function for call to object of type 'const primms_vertex::primms_distance'

One example of me calling the function is:

poke->mst_mode(poke->primms_vector, primms_vertex::primms_distance());

(the project is pokemon themed so excuse the funny class name) Both of the functors take in the exact same thing, 2 mst_vertex's, which is exactly what I am getting when I index into mst_vec. So I cannot figure out for the life of me what the compiler is complaining about. Any help would be appreciated!

Answer 1

Something like this:

#include <vector>

struct primms_vertex {
    bool been_visited{};
    size_t distance{};
    static size_t primms_distance(primms_vertex const& left, primms_vertex const& right);
};

size_t primms_vertex::primms_distance(primms_vertex const& left, primms_vertex const& right) {
    return left.distance < right.distance;
}

struct Poke {
    std::vector<primms_vertex> primms_vector;

    template <typename func>
    double mst_mode(std::vector<primms_vertex>& mst_vec, const func& comp) {
        size_t working_vertex{ 42 };
        for (size_t i = 0; i < mst_vec.size(); i++) {
            if (i != working_vertex && !mst_vec[i].been_visited && mst_vec[i].distance > comp(mst_vec[working_vertex], mst_vec[i])) {
                // do something.
            }
        }
        return 0.0;
    }

};

int main() {
    Poke* poke{}; // TODO: Instantiate a Poke.
    poke->mst_mode(poke->primms_vector, primms_vertex::primms_distance);
    return 0;
}