In his talk had a longer title, as it is really std::launder, std::start_lifetime_as, and UB in reinterpret_cast; OR... type punning done right. 

In this talk Javier Lopez-Gomez goes through all the trickery of low level casts for type punning and the dangers of ending up with undefined behavior. If you really need to do type punning this talk will give you a path to do it in the right way.

Video: Type punning done right - Javier Lopez Gomez - using std::cpp 2025