# enumerateObjects(at:options:using:) Executes a given block using the objects in the ordered set at the specified indexes. ``` func enumerateObjects(at s: IndexSet, options opts: NSEnumerationOptions = [], using block: (Any, Int, UnsafeMutablePointer) -> Void) ``` ## Parameters `s` The indexes of the objects over which to enumerate. `opts` A bitmask that specifies the options for the enumeration (whether it should be performed concurrently and whether it should be performed in reverse order). `block` The block to apply to elements in the ordered set. The block takes three arguments: - obj: The element in the ordered set. - idx: The index of the element in the ordered set. - stop: A reference to a Boolean value. The block can set the value to to stop further processing of the array. The `stop` argument is an out-only argument. You should only ever set this Boolean to within the block. ## Discussion By default, the enumeration starts with the first object and continues serially through the ordered set to the last element specified by `s`. You can specify [`concurrent`](/documentation/Foundation/NSEnumerationOptions/concurrent) and/or [`reverse`](/documentation/Foundation/NSEnumerationOptions/reverse) as enumeration options to modify this behavior. > Important: > If the block parameter or the `s` is `nil`, this method raises 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)