Hi Daryle, Good spot! This is definitely a bug. The documentation on Sequence should read something different (though what it ought to say is somewhat debatable…).
Could you file a bug on bugs.swift.org? Thanks! > On Dec 29, 2017, at 17:54, Daryle Walker via swift-users > <swift-users@swift.org> wrote: > > Sequence.underestimatedCount is supposed to work at O(1) time, according to > the docs on Apple’s developer website. On the other hand, Collection.count > works at O(n) time, except for RandomAccessCollection where it can work at > O(1) time. I’ve been playing around with creating various Collection types, > and it seem that their underestimatedCount has a default implementation that > just dumps to count, even when the latter is O(n)! > > I think that underestimatedCount should call count only for > RandomAccessCollection, while Collection and BidirectionalCollection call > isEmpty as needed. Is this a good idea? Should I post a bug report > (somewhere)? > > — > Daryle Walker > Mac, Internet, and Video Game Junkie > darylew AT mac DOT com > > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users
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