Feature gate: #![feature(iter_array_chunks)]

This is a tracking issue for Iterator::array_chunks, an iterator adapter that allows to group elements of an iterator.

Public API

// trait Iterator

fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>
where
    Self: Sized,self);

// core::iter

pub struct ArrayChunks<I: Iterator, const N: usize> { ... }

impl<I, const N: usize> ArrayChunks<I, N> {
    pub fn into_remainder(self) -> Option<array::IntoIter<I::Item, N>>;
}

impl<I: Iterator, const N: usize> Iterator for ArrayChunks<I, N> {
    type Item = [I::Item; N];
}

impl<I: DoubleEndedIterator + ExactSizeIterator, const N: usize> DoubleEndedIterator for ArrayChunks<I, N> {}
impl<I: FusedIterator, const N: usize> FusedIterator for ArrayChunks<I, N> {}
impl<I: ExactSizeIterator, const N: usize> ExactSizeIterator for ArrayChunks<I, N> {}

Steps / History

• Implementation: Add Iterator::array_chunks (take N+1) #100026
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• Should DoubleEndedIterator be implemented?
  • Is there a use-case for this?
  • In order to yield the same items either way we require ExactSizeIterator
  • Note that .rev().array_chunks() and .array_chunks().rev() are different
  • If we decide to keep DoubleEndedIterator implementation should be improved
    • For example, maybe there should be Iterator::next_chunk_back like there is for forward
  • Is the unwrap_err_unchecked in next_back_remainder sound, despite not using TrustedLen? (I didn't block the original PR on this because it goes through take, which I think we can trust, but I'd like someone smarter than me to think about it and confirm.)
• Should this be a type error for N != 0? (See also this same question in [T]::as_chunks.)
• What's the tradeoff between the item type being array::IntoIter<T, N> and the current one where the items are [T; N] and there's a remainder? ([T]::array_chunks has this question too and is unstable.)