fix Send / Sync (typos)

[sparecycles]

I think I found a couple copy-paste errors.

[sparecycles]

every other usage is in Send + Sync order.

[carllerche]

How does HashMap in std implement Send and Sync bounds?

[carllerche]

I actually don’t think that Iter can be Send because it holds a reference to the map. If I recall those bounds were intentional.

[sparecycles]

Hi @carllerche. I'm not sure if Iter should be Send or not.

But if that's the case, wouldn't Drain, IterMut, and ValueIterMut have the same bounds?

http/src/header/map.rs

Lines 2002 to 2003 in 8d45bd5

	unsafe impl<'a, T: Sync> Sync for IterMut<'a, T> {}
	unsafe impl<'a, T: Send> Send for IterMut<'a, T> {}

http/src/header/map.rs

Lines 2102 to 2103 in 8d45bd5

	unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}
	unsafe impl<'a, T: Send> Send for Drain<'a, T> {}

http/src/header/map.rs

Lines 2531 to 2532 in 8d45bd5

	unsafe impl<'a, T: Sync> Sync for ValueIterMut<'a, T> {}
	unsafe impl<'a, T: Send> Send for ValueIterMut<'a, T> {}

---

...

http/src/header/map.rs

Lines 1941 to 1942 in 8d45bd5

	unsafe impl<'a, T: Sync> Sync for Iter<'a, T> {}
	unsafe impl<'a, T: Sync> Send for Iter<'a, T> {}

[sparecycles]

@carllerche you're right! This pattern is also in the rust core libraries. Still feels like a typo (and if not, that it needs a nice fat comment).

https://github.com/rust-lang/rust/blob/917945d662c42053383fe3e71cb0f313d585e459/src/liballoc/collections/linked_list.rs#L1202-L1218

https://github.com/rust-lang/rust/blob/917945d662c42053383fe3e71cb0f313d585e459/src/libcore/slice/mod.rs#L2650-L2653

https://github.com/rust-lang/rust/blob/917945d662c42053383fe3e71cb0f313d585e459/src/libstd/collections/hash/table.rs#L916-L917

[sparecycles]

@carllerche You're right, the pattern of sync-implies-ref-is-send is deep in the rust type system.

[carllerche]

Would you mind adding a comment including your findings for the next person?

[sparecycles]

Well, I think I understand why Iter<T: Sync> is Sync + Send, but I don't understand why Iter<T: Send> is not Send, nor why IterMut/Drain etc... don't follow the same pattern.

If a good explanation appears in rust#53625, I'll can reopen this with a nice comment.