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koher 9/27/2018 2:14 AM
@swift-4.2.4 func foo<C: RangeReplaceableCollection>(_ collection: C) -> C.Index? { var collection = collection if collection.isEmpty { return nil} collection.removeFirst() return collection.startIndex } var a: Array<Int> = [2, 3, 5] var b: ArraySlice<Int> = a[...] print(foo(a)!) print(foo(b)!)