# \[Accepted\] SE-0052: Change IteratorType post-nil guarantee

**URL:** <https://forums.swift.org/t/accepted-se-0052-change-iteratortype-post-nil-guarantee/2463>\
**Category:** Announcements\
**Created:** [May 4, 2016, 11:27pm UTC](https://forums.swift.org/t/accepted-se-0052-change-iteratortype-post-nil-guarantee/2463 "2016-05-04T23:27:21Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Chris\_Lattner](https://avatars.discourse-cdn.com/v4/letter/c/bc8723/32.png) [@Chris\_Lattner](https://forums.swift.org/u/Chris_Lattner)\
**Post date:** [May 4, 2016, 11:27pm UTC](https://forums.swift.org/t/accepted-se-0052-change-iteratortype-post-nil-guarantee/2463/1 "2016-05-04T23:27:21Z")

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Proposal link: [swift-evolution/0052-iterator-post-nil-guarantee.md at master · apple/swift-evolution · GitHub](https://github.com/apple/swift-evolution/blob/master/proposals/0052-iterator-post-nil-guarantee.md)

Hello Swift Community,

The review of SE-0052: "Change IteratorType post-nil guarantee" ran from April 28...May 3, 2016. The proposal is \*accepted\* for Swift 3.

The feedback on this proposal was generally positive from the community and core team. The most significant concern was about performance: strengthening the requirement on IteratorType.next() could make some implementations of iterators slower. On the other hand, it does make some clients faster (UTF8 decoding being one cited case that demonstrates a big win). The core team believes that the improvements to performance in the most common use-cases will more than balance the reductions in performance for other cases.

Thank you to Patrick Pijnappel for proposing and implementing this!

-Chris  
Review Manager