サンプリング

public struct Sampling<Base: Collection, Selection: Collection>
where Selection.Element == Base.Index
extension Sampling: SamplingProtocol
extension Sampling: Collection
extension Sampling: BidirectionalCollection
  where Selection: BidirectionalCollection
extension Sampling: RandomAccessCollection
  where Selection: RandomAccessCollection

何らかの基本コレクションから、指定された順序で要素を遅延選択します。

`Selection`: `BidirectionCollection` で利用可能