Note to readers: This document is an early draft of a model for memory-safe references that I've been working on for the last ~2 years. While I think it is quite promising, the design is unfinished. The "regions" that I present in this document have not been given a formal semantics, and I have not explained where they originate from. My goal is merely to convince you that the design is promising, and that if seen to completion, it would advance the frontier of zero-cost memory safety.
Update August 2025: Verdagon has written an awesome blog post that explains this proposal at a high level. I recommend you check it out!
Update November 2025: The Carbon team is using this proposal as a starting point for their own memory safety model.
Update August 2026: Mojo 1.0 has adopted a variation of this proposal. See "Interior Origins" in the [Mojo 1.0 release notes](https://mojolang.or