Your packed union eliminates pure padding, yes, but it still costs 9 bytes to store a u8 value and misaligns accesses for wider elements. These are both signif

Your packed union eliminates pure padding, yes, but it still costs 9 bytes to store a u8 value and misaligns accesses for wider elements. These are both significant misses on "solving the problem." You also need to copy each element on access, which could be expensive for larger plain-old-data types, or especially for non-POD types.