lvalue_ref_example.cpp

#include <iostream>

template <int N>
struct Integer
{
    int& ref()
    {
        return x_;
    }
    Integer& add(int const x)
    {
        x_ += x;
        return *this;
    }
    Integer& operator+=(int const& x)
    {
        x_ += x;
        return *this;
    }
    int x_ = N;
};

template <int N>
::std::ostream& operator<<(::std::ostream& s, Integer<N> const& i)
{
    s << i.x_;
    return s;
}

int main()
{
    Integer<1> one;
    std::cout << one               // => 1
              << std::endl;

    Integer<2> two;
    std::cout << (two.add(6) += 4) // => 12
              << std::endl;

    Integer<3> three;
    three.ref() = 5;
    std::cout << three             // => 5
              << std::endl;

    Integer<4> four;
    std::cout << ((four += 4).add(16) += 4)
                                   // => 28
              << std::endl;
    return 0;
}