#include <iostream>
#include <memory> //shared_ptr
#include <map>
#include <vector>
#include <string>
 
class BaseFunctor{
public:
    virtual double operator()(std::vector<double> inputs) = 0;  
    virtual std::string name() = 0;  
};
 
class Sum : public BaseFunctor{
    double operator() (std::vector<double> inputs){ 
        double sum (0.0);
        for(auto elem : inputs)
            sum += elem;
        return sum;
    }
    std::string name() { return "sum"; }
};
 
class Prod : public BaseFunctor{
    double operator() (std::vector<double> inputs){ 
        double prod (1.0);
        for(auto elem : inputs)
            prod *= elem;
        return prod;
    }
    std::string name() { return "prod"; }
};
 
class Calculator {
private:
	using FPtr = std::shared_ptr<BaseFunctor>;
    std::map<std::string, FPtr> m_stats;
    std::vector<double> m_simple_data;
public:
    Calculator() 
        : m_simple_data({1.0, 2.0, 3.0}) {};
 
    void addStat(FPtr stat) { 
        m_stats.insert(std::pair<std::string, FPtr>(stat->name(), stat) ); 
    }
 
    double calc( std::string op_name){
    	return m_stats[op_name](m_simple_data);
    }
};
 
int main() {
 
    Calculator thing;
    thing.addStat(std::make_shared<Sum>());
    thing.addStat(std::make_shared<Prod>());
 
	std::vector<double> args {1.0, 2.0, 3.0};
	thing.calc("sum")
 
    return 0;
}