let a: [Int] = [2, 3, 5] let b = a.lazy let c = b.flatMap { [$0, $0] } print(type(of: c))
LazyCollection<FlattenBidirectionalCollection<LazyMapBidirectionalCollection<Array<Int>, Array<Int>>>>let a: [Int] = [2, 3, 5] let b = a.lazy let c = b.flatMap { [$0, $0] } print(type(of: c))
LazyCollection<FlattenBidirectionalCollection<LazyMapBidirectionalCollection<Array<Int>, Array<Int>>>>@escaping じゃない Sequence の flatMap 呼ぶのはどうすればいいんですっけ？