`chunk` like Iterators should panic on overflow

[Kerollmops]

Currently the Chunks, ChunksMut, ExactChunks and ExactChunksMut adapters does return None if an overflow occur in the Iterator::nth method.

I think this is not a good thing to have a silent "error", we must be consistent with other iterator adapters like enumerate and panic if an overflow is detected.

This has been talked in the tracking issue of the ExactChunks/Mut iterators adapters.

[cuviper]

https://doc.rust-lang.org/nightly/std/iter/trait.Iterator.html#method.nth

nth() will return None if n is greater than or equal to the length of the iterator.

None seems to be expected. A multiplication overflow here is just an internal side effect of requesting a too-large n, but I don't see why this should panic. We could equally check for n >= self.len() before attempting the multiplication, but that's actually more computational work.

[Kerollmops]

I agree with what you said.

The thing that bothered me is the fact that if it is not possible to access the chunk that produced an overflow with one nth call so it seems inconsistent to me that it can be accessed with two nth calls one after the other.

fn nth(&mut self, n: usize) -> Option<Self::Item> {
    let (start, overflow) = n.overflowing_mul(self.chunk_size);
    if start >= self.v.len() || overflow {
// ...

But it is not possible because if the multiplication has overflowed so it is likely that the accessed pointer is non addressable and so None must be returned.

So we can close this. Thank you for your time.

[cuviper]

Closing as suggested.