Rust’s Optional does close this altogether, yes. All (non-unsafe) users of Optional are required to have some defined behavior in both cases. This is enforced by the language in the match statement, and most of the “member functions” on Optional use match under the hood.
This is an issue with the C++ standardization process as much as with the language itself. AIUI when std::optional (and std::variant, which has similar issues) were defined, there was a push to get new syntax into the language itself that would’ve been similar to Rust’s match statement.
However, that never made it through the standardization process, so we ended up with “library variants” that are not safe in all circumstances.
This is an issue with the C++ standardization process as much as with the language itself. AIUI when std::optional (and std::variant, which has similar issues) were defined, there was a push to get new syntax into the language itself that would’ve been similar to Rust’s match statement.
However, that never made it through the standardization process, so we ended up with “library variants” that are not safe in all circumstances.
Here’s one of the papers from that time, though there are many others arguing different sides: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p00...