El crapo readonly attr

crap.cpp

#include <iostream>

class A
{
        public:
                A() : u(this->_v), _v(1) {}
                ~A() {}
        public:
                const int& u;
        private:
                int _v;
};

int main()
{
        A b;
        std::cout << b.u << std::endl;
        b.u++; // error!
        return 0;
}