Note that by creating the reference to a local and passing it up through the callback, you are using a fresh region that can’t possibly outlive any of one of th

Note that by creating the reference to a local and passing it up through the callback, you are using a fresh region that can’t possibly outlive any of one of the ones you are generic over. Fundamentally, that callback could stash the reference you pass it into state somewhere and now the pointer has escaped, invalidated as soon as that iteration of the loops ends. See that the definition of Group is tying those together. Instead, you can split them apart and maybe use HRTB to ensure the closure _must_ be able to treat the lifetime as fresh? But then you’ll probably have other issues… … which can largely be circumvented simply by pinning, in your reduced example, which probably doesn’t retain enough detail. https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=b05e99cce303001b0e10fda815369457 https://play.rust-lang.org/?version=stable&mode=debug&editio... My suggestion to avoid the pain? Use ArcStr.