[tutorial] Chain of responsibility pattern

#include <iostream>
#include <vector>
#include <functional>

struct Condiment
{
    std::function<std::string()> description;
    std::function<float()> price;
};

class Sugar
{
public:
    static std::string description() { return "-Sugar-"; }
    static float price() { return 0.07f; }
};

class Milk
{
public:
    static std::string description() { return "-Milk-"; }
    static float price() { return 0.13f; }
};

template<typename Call, typename NextCall>
static auto accu(Call call, NextCall next) -> decltype(call() + next())
{
    if (next) return call() + next();
    return call();
}


int main()
{
    Condiment condiments;
    condiments.description = [=] { return accu(&Milk::description, condiments.description); };
    condiments.description = [=] { return accu(&Sugar::description, condiments.description); };
    condiments.description = [=] { return accu(&Sugar::description, condiments.description); };

    condiments.price = [=] { return accu(&Milk::price, condiments.price); };
    condiments.price = [=] { return accu(&Sugar::price, condiments.price); };
    condiments.price = [=] { return accu(&Sugar::price, condiments.price); };

    std::cout << "Condiments: " << condiments.description() << '\n';
    std::cout << "Price: " << condiments.price() << '\n';

    return 0;
}