# indexOfObject(options:passingTest:) Returns the index of an object in the array that passes a test in a given block for a given set of enumeration options. ``` func indexOfObject(options opts: NSEnumerationOptions = [], passingTest predicate: (Any, Int, UnsafeMutablePointer) -> Bool) -> Int ``` ## Parameters `opts` A bit mask that specifies the options for the enumeration (whether it should be performed concurrently and whether it should be performed in reverse order). `predicate` The block to apply to elements in the array. The block takes three arguments: - obj: The element in the array. - idx: The index of the element in the array. - stop: A reference to a Boolean value. The block can set the value to to stop further enumeration of the array. If a block stops further enumeration, that block continues to run until it’s finished. When the `NSEnumerationConcurrent` enumeration option is specified, enumeration stops after all of the currently running blocks finish. The `stop` argument is an out-only argument. You should only ever set this Boolean to within the block. The block returns a Boolean value that indicates whether `obj` passed the test. ## Return Value The index whose corresponding value in the array passes the test specified by `predicate` and `opts`. If the `opts` bit mask specifies reverse order, then the last item that matches is returned. Otherwise, the index of the first matching object is returned. If no objects in the array pass the test, returns `NSNotFound`. ## Discussion By default, the enumeration starts with the first object and continues serially through the array to the last object. You can specify `NSEnumerationConcurrent` and/or `NSEnumerationReverse` as enumeration options to modify this behavior. > Important: > If the block parameter is `nil` this method will raise an exception. --- 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)