#include <iostream>

struct A {
    int a_;
    int b_;
    double c_;
    float d_;
    std::string e_;
};

struct B {
    int (A::*ref_);
    int value(const A& a) {
        return (a.*(this->ref_));
    }
};


template<typename TMember>
struct AccessorHolder {
    TMember (A::*ref_);

    const TMember& value(const A& a) const {
        return (a.*(this->ref_));
    }
};

int main() {
    B b{&A::a_};
    B c{&A::b_};
    A aa{5, 6, 7.0, 8.0, "karl lagerfeld"};
    std::cerr << b.value(aa) << ", " << c.value(aa) << std::endl;

    AccessorHolder<float> d{&A::d_};
    AccessorHolder<std::string> e{&A::e_};
    std::cerr << d.value(aa) << ", " << e.value(aa) << std::endl;
}