# prefix(while:) Republishes elements while a predicate closure indicates publishing should continue. ``` func prefix(while predicate: @escaping (Self.Output) -> Bool) -> Publishers.PrefixWhile ``` ## Parameters `predicate` A closure that takes an element as its parameter and returns a Boolean value that indicates whether publishing should continue. ## Return Value A publisher that passes through elements until the predicate indicates publishing should finish. ## Discussion Use [`prefix(while:)`](/documentation/Combine/Publisher/prefix(while:)) to emit values while elements from the upstream publisher meet a condition you specify. The publisher finishes when the closure returns `false`. In the example below, the [`prefix(while:)`](/documentation/Combine/Publisher/prefix(while:)) operator emits values while the element it receives is less than five: ``` let numbers = (0...10) numbers.publisher .prefix { $0 < 5 } .sink { print("\($0)", terminator: " ") } // Prints: "0 1 2 3 4" ``` --- 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)