{
  "$type": "site.standard.document",
  "bskyPostRef": {
    "cid": "bafyreifiwb4qgjoank6kybfluqtt753axouooryd3bgqjf4e24w52v475a",
    "uri": "at://did:plc:ivbknywyskln22er3nkssdhl/app.bsky.feed.post/3miprpl7stgw2"
  },
  "path": "/t/add-new-reserved-lifetime-owned/24129#post_1",
  "publishedAt": "2026-04-04T05:38:15.000Z",
  "site": "https://internals.rust-lang.org",
  "textContent": "Problem statement: Right now rust treats all owned types like String as having 'static lifetime, meaning rust in terms of borrow checking sees &'static str and String as same. This creates issues when we try to make a structure that is polymorphic over some type parameter S that could be a string slice reference or owned String.\n\nExample:\n\n\n    use std::marker::PhantomData;\n\n    trait AsStr<'s> {\n        fn to_str(self: &Self) -> &str;\n        fn from_str(s: &'s str) -> Self;\n    }\n\n    impl<'s> AsStr<'s> for &'s str {\n        fn to_str(self: &Self) -> &str {\n            *self\n        }\n\n        fn from_str(s: &'s str) -> Self {\n            s\n        }\n    }\n\n    impl<'s> AsStr<'s> for String {\n        fn to_str(self: &Self) -> &str {\n            self.as_str()\n        }\n\n        fn from_str(s: &'s str) -> Self {\n            s.to_string()\n        }\n    }\n\n    struct Check<'s, S: AsStr<'s>> {\n        s: S,\n        _v: PhantomData<&'s ()>\n    }\n\n    impl<'s1, S: AsStr<'s1>> Check<'s1, S> {\n        pub fn clone_to_owned(\n            self: &'s1 Self,\n        ) -> Check<'static, String>\n        {\n            Check {\n                s: self.s.to_str().to_string(),\n                _v: PhantomData::default()\n            }\n        }\n    }\n\n    fn example<'s, S: AsStr<'s>>(check: Check<'s, S>) -> Check<'static, String> {\n        check.clone_to_owned()\n    }\n\n\nLsp diagnostic errors:\n\n\n    Diagnostics:\n    1. `check` does not live long enough\n       borrowed value does not live long enough [E0597]\n    2. argument requires that `check` is borrowed for `'s` [E0597]\n    3. the parameter type `S` may not live long enough\n       ...so that the type `S` will meet its required lifetime bounds [E0309]\n\n\nProposed solution is owned lifetime that is allowed only for non-reference types, therefore any reference outlives 'owned, because we know that structure with 'owned type does not hold any references to initial data, making a copy.",
  "title": "Add new reserved lifetime: 'owned"
}