My little New Year’s Week project (and maybe one for you?)

[Updates: Clarified that an intrusive discriminator would be far beyond what most people mean by “C++ ABI break.” Mentioned unique addresses and common initial sequences. Added “unknown” state for passing to opaque functions.] Here is my little New Year’s Week project: Trying to write a small library to enable compiler support for automatic raw union member access checking. The problem, and what’s…