What's the status of feature try_reserve?

bettertree · February 7, 2026, 2:35pm

Tracking issue for `try_reserve`: RFC 2116 fallible collection allocation

opened 03:48AM - 07 Feb 18 UTC

A-allocators A-collections T-libs-api B-unstable B-RFC-implemented C-tracking-issue Libs-Tracked

This is a tracking issue for the `try_reserve` part of the RFC "fallible collect…ion allocation" (rust-lang/rfcs#2116). **Steps:** - [x] Implement the RFC #48648 - [x] Add `HashSet::try_reserve`: https://github.com/rust-lang/rust/pull/58623 - [x] Finalize the error type - [ ] Adjust documentation ([see instructions on forge][doc-guide]) - [ ] Stabilization PR ([see instructions on forge][stabilization-guide]) [stabilization-guide]: https://forge.rust-lang.org/stabilization-guide.html [doc-guide]: https://forge.rust-lang.org/stabilization-guide.html#updating-documentation **API:** ```rust impl /* each of String, Vec<T>, VecDeque<T> */ { pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {…} pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> {…} } impl /* each of HashMap<K, V> and HashSet<T> */ { pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {…} } /// The error type for `try_reserve` methods. #[derive(Clone, PartialEq, Eq, Debug)] pub enum TryReserveError { // in std::collections /// Error due to the computed capacity exceeding the collection's maximum /// (usually `isize::MAX` bytes). CapacityOverflow, /// The memory allocator returned an error AllocError { /// The layout of allocation request that failed layout: Layout, #[doc(hidden)] #[unstable(feature = "container_error_extra", issue = "0", reason = "\ Enable exposing the allocator’s custom error value \ if an associated type is added in the future: \ https://github.com/rust-lang/wg-allocators/issues/23")] non_exhaustive: (), }, } impl From<LayoutErr> for TryReserveError { fn from(_: LayoutErr) -> Self { TryReserveError::CapacityOverflow } } ```

Are TryReserveError::kind and TryReserveErrorKind the only blockers now?

Topic		Replies	Views
Try_reserve returning non-growable Vec view language design	9	971	July 14, 2021
Adding methods that returns errors when out of memory for collections libs	7	2948	March 25, 2019
Can we add `Layout` to `core::alloc::AllocError`? libs	5	876	July 18, 2022
Feedback from adoption of fallible allocations	17	3759	August 4, 2021
New String function `from_reserve` libs	14	944	July 16, 2021

What's the status of feature try_reserve?

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