Fatal error: Only BidirectionalCollections can be advanced by a negative amount

问题

How to convert an Array to a Set using Xcode Playground? We tried:

let a = Array(0 ..< 1000)
let s = Set(a)

This produces at run time:

Fatal error: Only BidirectionalCollections can be advanced by a negative amount

Issue happening with both Xcode 9.4 Playground and Xcode 10 beta 3 Playground.

回答1:

This is fixed in Xcode 10 beta 6 and newer, so I've updated the workaround to only apply for older swift versions.

---

For older Xcode versions (like Xcode 9.4), this may be caused by the number of elements being greater than 100.

Workaround found by Karoy Lorentey , is to customize Set's playground description:

#if !swift(>=4.2)
extension Set: CustomPlaygroundDisplayConvertible {
    public var playgroundDescription: Any {
        return description
    }
}
#endif

let a = Array(0 ..< 1000)
let s = Set(a)

Doing like that will not have error at run time.

来源：https://stackoverflow.com/questions/52128359/fatal-error-only-bidirectionalcollections-can-be-advanced-by-a-negative-amount