They're not only unsafe, but as far as I'm aware they're a compiler implementation detail that isn't really supposed to be used in user code (along with rustc_n

They're not only unsafe, but as far as I'm aware they're a compiler implementation detail that isn't really supposed to be used in user code (along with rustc_nonnull_optimization_guaranteed). It's actually how NonZero is implemented. See https://github.com/rust-lang/rust/blob/master/library/core/src/num/nonzero.rs https://github.com/rust-lang/rust/blob/master/library/core/s...