[swift-evolution] [Draft] Rename Sequence.elementsEqual

Kevin Nattinger swift at nattinger.net
Mon Oct 16 12:27:26 CDT 2017

>> How is the iteration order of an unordered set or dictionary “publicly observable”? If either is implemented such that it can asynchronously optimize its storage (maybe by rebalancing a tree or merging two non-contiguous array segments or something), its iteration order could change without changing what values it contains. Seems like consecutive calls to “elementsEquals” (or whatever we’re calling it) should return the same answer, if we don’t add, remove, or mutate elements.
> Sets are values. If you add, remove, or mutate any elements you have a different Set and thus a potentially different ordering of elements.

An implementation detail. We could make it a class* and AFAICT that wouldn't break any guarantees on Sequence; and the argument applies equally well to any other unordered Sequence, which has no value type or semantics constraint.

*: obviously we won't, I don't think anyone is advocating that.

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