`&Box<[T; N]>` doesn't impl `IntoIterator`

[programmerjake]

I tried this code:

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=04a2170785a4ddc68cf07d0757f41fb3

pub fn f(v: &Box<[String; 10]>) {
    for i in v {
        println("{i:?}");
    }
}

I expected to see this happen: compiles successfully and iterates over the boxed array.

Instead, this happened:

error[E0277]: `&Box<[String; 10]>` is not an iterator

Meta

rustc --version --verbose: (from playground)

1.97.0-nightly (2026-04-19 e22c616e4e87914135c1)

[programmerjake]

I think the appropriate fix is something like:

impl<T, const N: usize> !Iterator for [T; N] {} // if needed

impl<T, const N: usize, A: Allocator> IntoIterator for Box<[T; N], A> {
    type Item = T;
    type IntoIter = std::vec::IntoIter<T, A>; // we could use std::array::IntoIter, but that's less efficient

    fn into_iter(self) -> Self::IntoIter {
        Vec::<T, A>::from(self).into_iter()
    }
}

impl<'a, T, const N: usize, A: Allocator> IntoIterator for &'a Box<[T; N], A> {
    type Item = &'a T;
    type IntoIter = std::slice::Iter<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        self.iter()
    }
}

impl<'a, T, const N: usize, A: Allocator> IntoIterator for &'a mut Box<[T; N], A> {
    type Item = &'a mut T;
    type IntoIter = std::slice::IterMut<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        self.iter_mut()
    }
}

[Annonnymmousss]

@rustbot release-assignment

[WaffleLapkin]

I have a PR fixing this issue: #134021 (waiting on t-libs-api FCP)