{
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  "path": "/t/language-vision-regarding-safety-guarantees/24418#post_12",
  "publishedAt": "2026-06-30T12:51:00.000Z",
  "site": "https://internals.rust-lang.org",
  "textContent": "dlight:\n\n> I think it's best to ignore the logic thing and suppose that, even though currently it does not actually trigger UB, in the future, new semver-compatible versions of this API hold the right to trigger UB \"as promised\". So the API is _allowed_ to trigger UB when misused (and allowed to do anything else, including having a safe logic bug), but not required to do so at any given moment.\n\nThis is UB (library UB). It's the same situation as for builtin (language) UB: language UB is not _required_ to do anything particularly bad but it is _allowed_ to do anything it wants. Same thing for library UB. Being _allowed_ (but not required) to do arbitrary bad things is the very definition of UB.",
  "title": "Language vision regarding safety guarantees"
}