Returns the first element of the sequence that satisfies the given predicate.
SDK
- Xcode 9.0+
Framework
- Swift Standard Library
Declaration
func first(where predicate: (Key) throws -> Bool) rethrows -> Key?
Parameters
predicateA closure that takes an element of the sequence as its argument and returns a Boolean value indicating whether the element is a match.
Return Value
The first element of the sequence that satisfies predicate, or nil if there is no element that satisfies predicate.
Discussion
The following example uses the first(where:) method to find the first negative number in an array of integers:
let numbers = [3, 7, 4, -2, 9, -6, 10, 1]
if let firstNegative = numbers.first(where: { $0 < 0 }) {
print("The first negative number is \(firstNegative).")
}
// Prints "The first negative number is -2."
Complexity: O(n), where n is the length of the sequence.