Add documentation for `MaybeUninit<T>` by DanielEScherzer · Pull Request #2393 · rust-lang/reference

DanielEScherzer · 2026-10-20T18:32:35Z

No description provided.

…valid

DanielEScherzer · 2026-10-20T20:00:57Z

MaybeUninit guarantees:

ABI: Tracking issue for RFC 2645, "Transparent Unions" (formerly: and Enums) rust#60405 (RFC Transparent Unions and Enums rfcs#2645 had T-lang signoff)
size and alignment: stabilize core parts of MaybeUninit rust#60445 (T-lang and T-libs-api signoff)

So T-lang already agreed to these guarantees

Let's say this a bit more clearly. (The restatement in `undefined.validity.maybe-uninit` already reads OK.)

The placement of the new items didn't follow the ordering convention used in this list. Let's fix the placement of these.

The proposed wording here was taken from the documentation in the standard library. That text is a bit loose. It says that the type is "used to construct uninitialized values of type `T`", but of course we're using it to construct *initialized* values of type `T`, not *uninitialized* ones. And that's only one use case. It's indeed a bit tricky to concisely describe `MaybeUninit<T>`. Let's try to do a bit better.

traviscross · 2026-10-20T21:23:56Z

Thanks @DanielEScherzer.

Update books ## rust-lang/book 1 commits in 1500248d8f230566e4ec9f27fcbb8fe9e2898ab1..2771df165f092a4fbb9f46b5b2e7450f19010adb 2026-10-28 18:58:38 UTC to 2026-10-28 18:58:38 UTC - Upgrade to rust 1.99.1 (rust-lang/book#4861) ## rust-embedded/book 1 commits in 0789b0f29e73ecb91213cac10ad0eec1b9333770..637b4a0244e16ec391a60184ae0c86b550ffc24b 2026-10-27 19:19:19 UTC to 2026-10-27 19:19:19 UTC - Replace cty:: with core::ffi:: (rust-embedded/book#422) ## rust-lang/reference 1 commits in 2dafab96d919d6ab2884488e970bf95610ff83eb..3989fe91f1a601b51684a582ad17b2503f221787 2026-10-20 21:23:48 UTC to 2026-10-20 21:23:48 UTC - Add documentation for `MaybeUninit<T>` (rust-lang/reference#2393)

Rollup merge of #165364 - rustbot:docs-update, r=JohnTitor Update books ## rust-lang/book 1 commits in 1500248d8f230566e4ec9f27fcbb8fe9e2898ab1..2771df165f092a4fbb9f46b5b2e7450f19010adb 2026-10-28 18:58:38 UTC to 2026-10-28 18:58:38 UTC - Upgrade to rust 1.99.1 (rust-lang/book#4861) ## rust-embedded/book 1 commits in 0789b0f29e73ecb91213cac10ad0eec1b9333770..637b4a0244e16ec391a60184ae0c86b550ffc24b 2026-10-27 19:19:19 UTC to 2026-10-27 19:19:19 UTC - Replace cty:: with core::ffi:: (rust-embedded/book#422) ## rust-lang/reference 1 commits in 2dafab96d919d6ab2884488e970bf95610ff83eb..3989fe91f1a601b51684a582ad17b2503f221787 2026-10-20 21:23:48 UTC to 2026-10-20 21:23:48 UTC - Add documentation for `MaybeUninit<T>` (rust-lang/reference#2393)

rustbot added the S-waiting-on-review Status: The marked PR is awaiting review from a maintainer label Oct 20, 2026

DanielEScherzer force-pushed the MaybeUninit branch from ddd61cc to 77242cd Compare October 20, 2026 18:36