Rust's "raw" way to spell all symbols is clever. Maybe some day my function named weigh will be a problem because of a new "weigh" keyword. Rust gets to add the keyword but still talk about my function in new editions by just spelling the symbol awkwardly, as r#weigh. This forbids Rust from reserving such spellings (e.g. "r#weigh") as keywords themselves, but that would be so ugly nobody would want to do it. Overall the result is Rust 2021 could even make "new" a keyword if it wanted to, and the old code which uses that symbol name everywhere still works, it's just a little clumsy to talk to it from next edition code.

Still, I think it's worth remembering that the edition changes in Rust so far have been much smaller than many changes contemplated for C++ Epochs (or any hypothetical actual C++ feature similar to Vittorio's proposal in spirit).

C++ has a lot of problems, and understandably Epoch proponents want to do stuff like ban implicit narrowing coercions, or change how overflow works. Because of how sprawling C++ is these are surprisingly big changes to the whole language, and I don't think that you could pull off something like that with editions.

I have a hopeful note though. Maybe C++ can inspire a much more powerful tool than editions, somehow enabling backward compatibility for C++ while also allowing new C++ to be written exclusively in Stroustrup's "subset of a superset" that keeps most of C++'s strengths but loses so much baggage like implicit coercions everywhere. If it's possible, the C++ community have the right people.