https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80652
--- Comment #6 from Peter Boyle <paboyle at ph dot ed.ac.uk> --- Just a comment -- suggest a warning thrown if union access from two views is made. AFAIK g++ is the only compiler not implementing the defacto type pun use. http://en.cppreference.com/w/cpp/language/union "Many compilers implement, as a non-standard language extension, the ability to read inactive members of a union." i.e. warn on attempted use of the above behaviour.
