C++ versions are practically a new language. Last two Rust editions required no changes on any of my code. Why are people constantly harping on this obviously untrue idea. New Rust versions and editions make the language _simpler_.
This juxtaposition kind of makes it seem like that new C++ versions did require changes to your code, did they?
My understanding is that C++ maintains backwards compatibility.
My code went from 2015 to 2018 and 2021 by simply changing Cargo.toml. No code changes were necessary and it was still completely idiomatic code. Nothing was deprecated or even outdated.
An idiomatic C++11 solution is not likely to be the idiomatic C++17 solution however. Every version of C++ makes deep changes to the actual language and adds a ton of features. Whereas Rust versions and editions tend to make the language simpler as they generally remove limitations.
It's true that there are usually new features which arguably make older code no longer idiomatic, but modernizing code is always optional, so what's really the issue there?