Type aliasing (use of more then one type for essentially the same data) is a huge problem in C++. If you keep member functions out of structs and maintain them as PODs, things ought to work. But
static_assert(sizeof(vec) == sizeof(float) * 3);
can't make accessing one type as another technically legal. In practice of course there will be no padding, but C++ isn't clever enough to realise that vec is an array of floats and an array of vecs is an array of floats constrained to be a multiple of three, and the casting &vecasarray[0] to a vec * is legal but casting &vecasarray[1] is illegal.
