protocol _SequenceWrapper A type that is just a wrapper over some base Sequence Inheritance View Protocol Hierarchy → Associated Types Base : Sequence Iterator : IteratorProtocol = Self.Base.Iterator Import import Swift Default Implementations Where Self : Sequence, Iterator == Base.Iterator var underestimatedCount: Int Returns a value less than or equal to the number of elements in the sequence, nondestructively. Complexity: O(n), where n is the length of the sequence if the sequence is a collection or wraps a collection; otherwise, O(1). Declaration var underestimatedCount: Int { get }