5.3 で Implemented になってた RangeSet https://github.com/apple/swift-evolution/blob/master/proposals/0270-rangeset-and-collection-operations.md が revert された。

apple/swift-evolution

This maintains proposals for changes and user-visible enhancements to the Swift Programming Language. - apple/swift-evolution

1:02 AM

https://github.com/apple/swift/pull/31827

[5.3] Revert RangeSet additions by natecook1000 · Pull Request #318...

Don’t push RangeSet into 5.3 since the additions are all available via the preview package. This will give it more time to bake. rdar://problem/63285386