Pre-RFC improved ergonomics for `!`

robofinch:

Imagine that someone had UninhabitedErr<T, E>(Result<T, E>) whose safety invariant is that E is an uninhabited 1-aligned ZST, as enforced by unsafe constructors?

That's a good example. I've bookmarked for later (if there is a later).

If I understand correctly: constructing an UninhabitedErr<T, E> would be unsafe. Which would make the validation simple: can both types be constructed without unsafe.

robofinch:

(Note: I have my “library author” hat on, I’m not a compiler dev. So, I’m used to being very paranoid to attempt to write bulletproof unsafe code, while the compiler devs probably have a better grasp of what sorts of code actually exist out there, and the language does occasionally make breaking changes after a lot of communication.)

I'm also coming at this as a library author with a similar view of unsafe . And "could break unsafe code" has been the killer for any previous attempts to look at this - which is a stance I'm not going to challenge (both because I agree with it and I don't have anywhere the background to do so)