Currently, the lifetime elision doc only documents function definitions, but lifetime elision is also allowed in the following other locations:
* `fn` types, such as `fn(&T)`
* `Fn`/`FnMut`/`FnOnce`, such as `Fn(&T)`
* `impl` headers
To demo this up, I made some type aliases for `fn`/`Fn` which you can pass `&T` as a parameter to (to follow the lifetime rules of the surrounding context), and compared what you get with that instead of using `fn`/`Fn` directly, where lifetime elision takes on the rules from `fn`/`Fn`/etc.
I also demoed up an `impl` header that used lifetime elision twice, although the error message in that case is broken (filed https://github.com/rust-lang/rust/issues/87763)
The demo was half for this change description, and half just to make sure I understand Rust -- in particular, I really had to reverse engineer it for `impl` because I wasn't sure, and it didn't seem to be documented anywhere (at least not here!)
https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=f82b280de4b992f225bc32121f333e96
Devin Jeanpierre
Yuki Okushi
portal
Steve Klabnik