Maybe optional actions (fn action_var(&amp;mut self, var: &amp; Var) -> Option<var>) can be take argument by value if you roundtrip it back?

fn action_var(&amp;mut self, var: Var) -> Var</var>

hyper-util

It is not released to crates.io as of now, even as alpha version.

Update: now it is released. docs.rs does not show anything yet. There is a pull request about it already though.