offset_of_slice
The tracking issue for this feature is: #126151
When the offset_of_slice feature is enabled, the offset_of! macro may be used to determine
the offset of fields whose type is [T], that is, a slice of dynamic size.
In general, fields whose type is dynamically sized do not have statically known offsets because
they do not have statically known alignments. However, [T] has the same alignment as T, so
it specifically may be allowed.
#![feature(offset_of_slice)] #[repr(C)] pub struct Struct { head: u32, tail: [u8], } fn main() { assert_eq!(std::mem::offset_of!(Struct, tail), 4); }