SE-0459: Add Collection conformances for enumerated()

Evolution Proposal Reviews
1

Hi Swift community,

The review of SE-0459: Add Collection conformances for enumerated() begins now and runs through 7th of February, 2025.

This is a subsetted proposal previously part of SE-0312, which was returned for revision following issues with the zip aspect of the proposal. This proposal only includes the conformance for enumerated().

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Thank you,

Ben Cohen
Review Manager

14 Likes
2

Adding a comment as reviewer, not in my capacity as review manager:

Having read the alternative considered, I believe it would be better to only conform to BidirectionalCollection when the underlying collection is a RandomAccessCollection, in order to preserve constant-time access to the last index.

I appreciate that the O(n) cost is only on accessing the last index, not subsequently moving that index backwards, so that cost can be amortized over e.g. a full reversal. But while overall complexity of algorithms generally trumps constant time factors, I do think those constant time factors still matter and so shouldn't be waved away lightly. And it is entirely possible that functions generic over BidirectionalCollection might access the last element multiple times, considering it free, and so might incur the linear traversal cost more than once.

15 Likes
3

Much as I hate to curtail this heated discussion, the proposal has been accepted with modifications.

13 Likes