Xcode 9 and Xcode 10 giving different results, even with same swift version

Question

I am running this code in both xcode 9.3 and xcode 10 beta 3 playground

import Foundation

public protocol EnumCollection: Hashable {
    static func cases() -> AnySequence<Self>
}

public extension EnumCollection {

    public static func cases() -> AnySequence<Self> {
        return AnySequence { () -> AnyIterator<Self> in
            var raw = 0
            return AnyIterator {
                let current: Self = withUnsafePointer(to: &raw) { $0.withMemoryRebound(to: self, capacity: 1) { $0.pointee } }

                guard current.hashValue == raw else {
                    return nil
                }

                raw += 1
                return current
            }
        }
    }
}

enum NumberEnum: EnumCollection{
    case one, two, three, four
}

Array(NumberEnum.cases()).count

even though both are using swift 4.1 they are giving me different results for the

on xcode 9.3 the size of array is 4

and on xcode 10 beta 3 the size of array is 0

I don't understand this at all.

Answer 1

That is an undocumented way to get a sequence of all enumeration values, and worked only by chance with earlier Swift versions. It relies on the hash values of the enumeration values being consecutive integers, starting at zero.

That definitely does not work anymore with Swift 4.2 (even if running in Swift 4 compatibility mode) because hash values are now always randomized, see SE-0206 Hashable Enhancements:

To make hash values less predictable, the standard hash function uses a per-execution random seed by default.

You can verify that with

print(NumberEnum.one.hashValue)
print(NumberEnum.two.hashValue)

which does not print 0 and 1 with Xcode 10, but some other values which also vary with each program run.

For a proper Swift 4.2/Xcode 10 solution, see How to enumerate an enum with String type?:

extension NumberEnum: CaseIterable  { }
print(Array(NumberEnum.allCases).count) // 4