# LazyPrefixWhileSequence A sequence whose elements consist of the initial consecutive elements of some base sequence that satisfy a given predicate. ``` @frozen struct LazyPrefixWhileSequence where Base : Sequence ``` ## Overview> Note: When `LazyPrefixWhileSequence` wraps a collection type, the > performance of accessing `endIndex` depends on how many > elements satisfy the predicate at the start of the collection, and might > not offer the usual performance given by the `Collection` protocol. > Accessing `endIndex`, the `last` property, or calling methods that > depend on moving indices might not have the documented complexity. ## Topics ### Type Aliases [`typealias Element`](/documentation/Swift/LazyPrefixWhileSequence/Element) A type representing the sequence’s elements. ### Default Implementations [BidirectionalCollection Implementations](/documentation/Swift/LazyPrefixWhileSequence/BidirectionalCollection-Implementations) [Collection Implementations](/documentation/Swift/LazyPrefixWhileSequence/Collection-Implementations) [LazySequenceProtocol Implementations](/documentation/Swift/LazyPrefixWhileSequence/LazySequenceProtocol-Implementations) [Sequence Implementations](/documentation/Swift/LazyPrefixWhileSequence/Sequence-Implementations) ## Relationships ### Conforms To [`LazySequenceProtocol`](/documentation/Swift/LazySequenceProtocol) [`Copyable`](/documentation/Swift/Copyable) [`Escapable`](/documentation/Swift/Escapable) [`Collection`](/documentation/Swift/Collection) [`LazyCollectionProtocol`](/documentation/Swift/LazyCollectionProtocol) [`Sequence`](/documentation/Swift/Sequence) [`BidirectionalCollection`](/documentation/Swift/BidirectionalCollection) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)