Tracking issue for chunks_exact/_mut; slice chunks with exact size · Issue #47115 · rust-lang/rust (original) (raw)

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Description

This is inspired by ndarray and generally seems to allow llvm to remove more bounds checks in the code using the iterator (because the slices will always be exactly the requested size), and doesn't require the caller to add additional checks.

A PR adding these for further discussion will come in a bit.

• Implemented in Add slice::ExactChunks and ::ExactChunksMut iterators #47126

Open questions:

• Should the new iterators panic if the slice is not divisible by the chunk_size, or omit any leftover elements.
  The latter is implemented right now and very similar to how zip works and @shepmaster even argues that without this, this iterator is kind of useless and the optimization should be implemented as part of the normal chunks iterator (which seems non-trivial, see ).
  Omission of leftover elements is also how this iterator is implemented in ndarray (but far more general).

A function for getting access to the remainder exists on the iterator, similar to how `slice::Iter` and `slice::IterMut` give access to the tail (note: the remainder are the odd elements that don't completely fill a chunk, it's not the tail!)
**The majority of people (who spoke up here) seem to prefer the non-panicking behaviour**

- [x] Should it be called `exact_chunks` or `chunks_exact`? The former is how it's called in `ndarray`, the latter is [potentially more discoverable](https://github.com/rust-lang/rust/issues/47115#issuecomment-403090815) in e.g. IDEs.
**It was renamed to `chunks_exact`**