@swiftbot --versions=3.0.1,3.0.2,3.1,3.1.1

extension Sequence { public func flatten<T>() -> [T] where Iterator.Element : Sequence, Iterator.Element.Iterator.Element == T { return flatMap { $0 } } } let a: [[Int]] = [[2, 3], [5]] let b: [Int] = a.flatten() print(b)