bring back `zip` methods

[baloo]

See example usage: https://github.com/RustCrypto/AEADs/blob/d1a22983d2af3c6a1ac3644850351f0ab0a77e51/eax/src/online.rs#L352

[baloo]

The only purpose of using a trait here is to limit API breakage with generic-array but it's otherwise not required.

Now I comment on it, I kind of feel I should have gone with a straight impl Array block. Opinion?

[tarcieri]

Yes, these should just be inherent methods. GenericArray was weird for defining traits for everything, being the only implementor, and then writing blanket impls, which only makes it annoying to pull those traits into scope.

No unsafe code should be required for any of these. You should be able to leverage the FromIterator/IntoIterator impls, either on core arrays or on Array, e.g. Array::map can be written Array(self.0.map(f)).

It'd also be good to update the migration guide.

[tarcieri]

Perhaps we can just add Array::map and for zip and join suggest using IntoIterator instead in the migration guide: https://github.com/RustCrypto/hybrid-array/blob/b362ec7/src/lib.rs#L66

[tarcieri]

map looks good, but zip seems weird to me, as in there's [T; N]::map defined in core, but no corresponding zip method in core.

I'm not sure this really deserves its own module either, especially if it's just map.

[baloo]

well, we could do a into_iter().zip(other_array) but this doesn't strictly enforces the size which would be missing. https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.zip.

I don't know how to write a migration guide without just copy pasting this implementation every time.

[tarcieri]

Where is it actually being used?

If we do add it, I think it should be deprecated.

[baloo]

generic-array: https://github.com/RustCrypto/AEADs/blob/d1a22983d2af3c6a1ac3644850351f0ab0a77e51/eax/src/online.rs#L352

hybrid-array (earlier implementation): https://github.com/RustCrypto/AEADs/blob/00dbd8a8d15895a6df8759b2fbf7025b2c57eb52/eax/src/online.rs#L352

[tarcieri]

Yikes, that's gross!

let full_tag = self.nonce.zip(h, |a, b| a ^ b).zip(c, |a, b| a ^ b);
Tag::<M>::clone_from_slice(&full_tag[..M::to_usize()])

It looks like it could be replaced by something like:

self.nonce.into_iter().zip(h, |a, b| a ^ b).take(M::to_usize()).collect()

[tarcieri]

I guess I should also mention: one of the goals of hybrid-array is to be shaped a lot closer to core arrays, to aid an eventual transition to core arrays.

I would prefer not to continue to provide generic-array esoterisms, and if we do they should only be to aid a transition, and deprecated.

[baloo]

the only benefit I've seen from having a zip implementation was the enforcement of the sizes.

But in the case of eax, this is enforced externally (message and data being the same size / type). Yeah. I guess we can go with the into_iter()

[tarcieri]

FWIW bringing back map still seems good to me

[baloo]

well, it was in your branch? I didn't a use for it quite yet.

[tarcieri]

I don't have a branch

[baloo]

https://github.com/RustCrypto/hybrid-array/tree/array-map ??