Add example for Lifetime Elision with two inputs.

[snowe2010]

Lifetime elision with two input references is not clear.
Closes #21284

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @huonw (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see CONTRIBUTING.md for more information.

[huonw]

r? @steveklabnik

[steveklabnik]

This is now out of date, and needs a rebase.

[snowe2010]

I was waiting for input on my comment. What should I change the question mark to?

[Gankra]

I think just leaving the questionmark off should be sufficient in context.

That is, just -> &str

[snowe2010]

r=steveklabnik I think it's ready, let me know if I need to clean anything up. Also, not sure if I did the r= bit right.

[steveklabnik]

You can't add the r, only people with permission can :)

I think the rebase went wrong here, there's a tooon of unrelated commits.

[snowe2010]

I'm not seeing any unrelated commits? Where exactly do you see them?

[Gankra]

[snowe2010]

@gankro, those were there before I rebased. I saw them show up like 2 days before I rebased. I didn't do any of that. You can check from my commit history on my repo too. Don't know how those got there.

[snowe2010]

This has been moved to #21618 due to (maybe) Github problems and the fact that this PR somehow won't update anymore from my fork.