Implement From<Array<A, D>> for ArcArray<A, D>

[jturner314]

I'd like to make CowRepr implement DataOwned, where DataOwned is changed to mean "a storage type which can own its data". The only issue is the .into_shared() method, which says, "Turn the array into a shared ownership (copy on write) array, without any copying." We can't always turn a CowArray into an ArcArray without copying. One approach (which would be a breaking change) would be to remove DataOwned::into_shared and just rely on this From implementation instead. Then, we could implement DataOwned for CowRepr without issues.

Regardless of the CowRepr stuff, this impl still seems useful.

[bluss]

Agree. I hope to keep the into_shared etc methods somehow, but it's clear that they need to change to support wider diversity of owned arrays (including future differences in allocator). Maybe adding a Clone bound to into_shared() would be ok and sufficient, and then the specific From impls can be used by users when they need to avoid Clone requirements.

[jturner314]

Maybe adding a Clone bound to into_shared() would be ok and sufficient, and then the specific From impls can be used by users when they need to avoid Clone requirements.

Yeah, I think this makes the most sense. We'd move into_shared from DataOwned to Data, add an A: Clone bound, and drop the "without any copying" guarantee. In most cases, the user would just use .into_shared() to convert arrays to ArcArray (so that all they'd need is are A: Clone and S: Data bounds), but if they want to create an ArcArray from an array without A: Clone, they would use an Into<ArcArray> bound instead.