Tracking Issue for `const_array`

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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_map be constified

Footnotes

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩

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@rustbot label -S-tracking-unimplemented

[syberant]

Hi! Just ran into a usecase for this: generating a const lookup 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) and array::try_map (#79711) are both still unstable in non-const contexts I would personally like to only try to stabilise const array::from_fn and array::map.

Kind of new to this, is there anything preventing this from proceeding to FCP?

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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.