Anonymous union and struct [duplicate]

Answer 1

Anonymous unions are allowed in C++11/14. See the example of their usage at Bjarne Stroustrup's C++11 FAQ

Regarding anonymous structs see Why does C++11 not support anonymous structs, while C11 does? and Why does C++ disallow anonymous structs and unions?

Though most compilers support anonymous structs, if you want your code to be standard compliant you have to write something like this:

template 
struct vec
{
    union {
       struct { some_type x, y, z; } s1;
       struct { some_type r, g, b; } s2;

       some_type elements[3];
    };
};