What was being discussed upthread went a lot further than what you're talking about. The string concat thing is a specific piece of ordinary static analysis that any language with a compile stage can perform. It's also pretty trivially defeated in ways that crop up in real code. I'm not saying it isn't useful, I'm saying it's nowhere close to what would be required to render the performance costs of doing strings the Java way equivalent to the Rust way. Therefore, to go even further upthread, Rust still provides a meaningful choice, trading Java's convenience for Rust's performance.