# classes(for:argumentIndex:ofReply:) Returns the current list of allowed classes that can appear within the specified collection object argument to the specified method. ``` func classes(for sel: Selector, argumentIndex arg: Int, ofReply: Bool) -> Set ``` ## Parameters `sel` Specifies which method in the protocol you want information about. `arg` Specifies the position (starting at index 0) of the parameter for which you want to obtain the current set of allowed classes. This may be either the position of a parameter in the method itself or the position in its reply block. `ofReply` Pass if `arg` is an index into the parameters of the reply block, or if it is an index into the parameters of the method itself. ## Discussion See [`setClasses(_:for:argumentIndex:ofReply:)`](/documentation/Foundation/NSXPCInterface/setClasses(_:for:argumentIndex:ofReply:)) for more explanation. ## See Also [Daemons and Services Programming Guide](https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/Introduction.html#//apple_ref/doc/uid/10000172i) --- 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)