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  "path": "/t/idea-trait-methods-with-un-overridable-implementations/23906?page=2#post_25",
  "publishedAt": "2026-03-12T06:00:48.000Z",
  "site": "https://internals.rust-lang.org",
  "tags": [
    "github.com/rust-lang/rust",
    "`final` methods should work the same as without it (if it works without it)",
    "mu001999",
    "play"
  ],
  "textContent": "github.com/rust-lang/rust\n\n####  `final` methods should work the same as without it (if it works without it)\n\nopened 09:31AM - 10 Mar 26 UTC\n\n mu001999 \n\nI-unsound  C-bug  T-types  A-dyn-trait  F-final_associated_functions\n\nTracking: https://github.com/rust-lang/rust/issues/131179 Found when trying to …use `final` to impl `Error::type_id` in https://github.com/rust-lang/rust/pull/153598, this code (play) doesn't work as expected: ```rust #![feature(final_associated_functions)] trait Tr where Self: 'static, { final fn foo(&self) -> std::any::TypeId { std::any::TypeId::of::<Self>() } } struct Foo; impl Tr for Foo {} struct Bar; impl Tr for Bar {} fn foo(t: &dyn Tr) -> std::any::TypeId { t.foo() } fn main() { assert_ne!(foo(&Foo), foo(&Bar)); } ``` I expected to see this happen: run successfully Instead, this happened: assertion failed. And without `final`, this will run as expected. ### Meta ``` Build using the Nightly version: 1.96.0-nightly (2026-03-09 2d76d9bc76f27b03b489) ```",
  "title": "Idea: trait methods with un-overridable implementations"
}