---
title: "prefix(while:)"
framework: swift
role: symbol
role_heading: Instance Method
path: "swift/uint/words-swift.struct/prefix(while:)"
---

# prefix(while:)

Returns a subsequence containing the initial elements until predicate returns false and skipping the remaining elements.

## Declaration

```swift
func prefix(while predicate: (Self.Element) throws -> Bool) rethrows -> Self.SubSequence
```

## Parameters

- `predicate`: A closure that takes an element of the sequence as its argument and returns true if the element should be included or false if it should be excluded. Once the predicate returns false it will not be called again.

## Discussion

Discussion note: O(n), where n is the length of the collection.