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Tracking Issue for const_array #147606
Description
Feature gate: #![feature(const_array)]
This is a tracking issue for const [T]::map and array::from_fn.
Public API
// core::array
impl<T, const N: usize> [T; N] {
pub const fn map<F, U>(self, f: F) -> [U; N]
where
F: [const] FnMut(T) -> U + [const] Destruct,
U: [const] Destruct;
}
pub const fn from_fn<T: [const] Destruct, const N: usize, F>(f: F) -> [T; N]
where
F: [const] FnMut(usize) -> T + [const] Destruct;Steps / History
(Remember to update the S-tracking-* label when checking boxes.)
- Implementation: constify from_fn, try_from_fn, try_map, map #147071
- Final comment period (FCP)1
- Stabilization PR
Unresolved Questions
- Should
array::try_mapbe constified
Activity
bend-n commentedon Feb 7, 2026
@rustbot label -S-tracking-unimplemented
syberant commentedon Aug 27, 2026
Hi! Just ran into a usecase for this: generating a
constlookup table from another array.My workaround for stable Rust was some ugly code involving a new array whose elements I completely replace in a while loop.
Given that
array::try_from_fn(#89379) andarray::try_map(#79711) are both still unstable in non-const contexts I would personally like to only try to stabilise constarray::from_fnandarray::map.Kind of new to this, is there anything preventing this from proceeding to FCP?
bend-n commentedon Aug 27, 2026
This feature is kind of very far from stabilization, as it depends, primarily, on #143874, which is not very close to stabilization, and not only that but to be useful it requires #106003. To use this on stable you'd have to use some macro based solution.