Just pass `Layout` directly to `box_new_uninit` *[View all comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust/pull/152737)* We have a constant for it already (used in `RawVec` for basically the same polymorphization) so let's use it. This is a simple follow-up to rust-lang/rust#148190 from one of the comments.