union {
    {
        Scalar x, y;
    }
    Scalar v[2];
};

union {
    struct {
        int x;
        int y;
    };
    int v[2];
};

union a {
    struct b { int first, second; } bee;
    int v[2];
};

template<class T>
struct U1
{
    U1();
    T   v[2];
    T&  x;
    T&  y;
};

template<class T>
U1<T>::U1()
    :x(v[0])
    ,y(v[1])
{}

int main()
{
    U1<int>   data;

    data.x  = 1;
    data.y  = 2;
}

struct Vec2
{
  float x;
  float y;
  float& operator[](int i) { return *(&x+i); }
};