# Lookahead A regex component that allows a match to continue only if its contents match at the given location. ``` struct Lookahead

``` ## Overview A lookahead is a zero-length assertion that its included regex matches at a particular position. Lookaheads do not advance the overall matching position in the input string — once a lookahead succeeds, matching continues in the regex from the same position. ## Topics ### Initializers [`init(() -> R)`](/documentation/RegexBuilder/Lookahead/init(_:)-2yv8x) Creates a lookahead from the regex generated by the given builder closure. [`init(R)`](/documentation/RegexBuilder/Lookahead/init(_:)-4s5w2) Creates a lookahead from the given regex component. ## Relationships ### Conforms To [`Escapable`](/documentation/Swift/Escapable) [`Copyable`](/documentation/Swift/Copyable) [`RegexComponent`](/documentation/Swift/RegexComponent) --- 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)