Is it possible to share your code that would need to use these impls? I have not come across Reverse<T> needing to be serialized.

I see it as a very convenient way to serialize a sorted collection in the reverse order. Like this:

let mut my_coll = BTreeSet::new();
my_coll.insert(Reverse(1));
my_coll.insert(Reverse(2));
my_coll.insert(Reverse(3));

assert_eq!(serde_json::to_string(&my_coll).unwrap(), "[3, 2, 1]");

Thanks, that's fair. You will need to add a build flag in build.rs because core::cmp::Reverse is new in 1.19.0 and we support back to 1.13.0.

@dtolnay Done.

Released in 1.0.89.