LazyCollectionProtocol
protocol LazyCollectionProtocol : Collection, LazySequenceProtocol where Self.Elements : CollectionSupertypes
protocol CollectionA sequence whose elements can be traversed multiple times, nondestructively, and accessed by an indexed subscript.
protocol LazySequenceProtocolA sequence on which normally-eager sequence operations are implemented lazily.
protocol SequenceA type that provides sequential, iterated access to its elements.