RevSlice requires repr(C) or repr(transparent)

[dtolnay]

Without one of those attributes, my understanding is the transmute from &[T] to &RevSlice<T> is undefined behavior. The compiler is free to stick some additional data at the start of RevSlice<T> or give it a stricter alignment than [T]. For example some targets may require all struct types to have some minimum alignment that is not required for slices.

From nomicon's Alternative representations:

#[repr(C)] is also necessary to soundly do more elaborate tricks with data layout such as reinterpreting values as a different type.

[scottmcm]

Yes, that's theoretically true right now, but it may very soon not be: rust-lang/unsafe-code-guidelines#31 (comment)

[scottmcm]

Made it transparent in 0.1.4.

rev_slice/src/lib.rs

Lines 65 to 68 in b555bcd

	/// A DST newtype providing a reversed view of a slice.
	#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
	#[repr(transparent)]
	pub struct RevSlice<T>([T]);