alt Hacker NewsI wouldn't say it's impossible, rather un-ergonomic. TypeScript can add type information to ordinary JavaScript code via JSDoc comments; the result can both be executed as ordinary JavaScript as-is and type-checked with TypeScript. But it's a huge pain to try to write (and maintain) everything that way, it was supported as a hack to help migrate legacy codebases. You could probably take a similar "the lifetimes are embedded in comments" approach with other languages, and the result would be similarly un-ergonomic.
That is possible (clang has experimental lifetime annotations support), but that is not enough to guarantee memory safety.
As a simple example, Zig has no private fields. That makes encapsulating any unsafety impossible.