#![feature(rustc_attrs)] #![allow(unused,dead_code)] fn nested_field() { #[rustc_layout_scalar_valid_range_start(1)] struct NonZero(T); let mut foo = unsafe { NonZero((1,)) }; foo.0.0 = 0; //~^ ERROR: mutation of layout constrained field is unsafe } fn block() { #[rustc_layout_scalar_valid_range_start(1)] struct NonZero(T); let mut foo = unsafe { NonZero((1,)) }; { foo.0 }.0 = 0; // ^ not unsafe because the result of the block expression is a new place } fn main() {}