# class_replaceMethod(_:_:_:_:) Replaces the implementation of a method for a given class. ``` func class_replaceMethod(_ cls: AnyClass?, _ name: Selector, _ imp: IMP, _ types: UnsafePointer?) -> IMP? ``` ## Parameters `cls` The class you want to modify. `name` A selector that identifies the method whose implementation you want to replace. `imp` The new implementation for the method identified by `name` for the class identified by `cls`. `types` An array of characters that describe the types of the arguments to the method. For possible values, see [Objective-C Runtime Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40008048) > [Type Encodings](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html#//apple_ref/doc/uid/TP40008048-CH100). Since the function must take at least two arguments—`self` and `_cmd`, the second and third characters must be “`@:`” (the first character is the return type). ## Return Value The previous implementation of the method identified by `name` for the class identified by `cls`. ## Discussion This function behaves in two different ways: - If the method identified by `name` does not yet exist, it is added as if [`class_addMethod(_:_:_:_:)`](/documentation/ObjectiveC/class_addMethod(_:_:_:_:)) were called. The type encoding specified by `types` is used as given. - If the method identified by `name` does exist, its IMP is replaced as if [`method_setImplementation(_:_:)`](/documentation/ObjectiveC/method_setImplementation(_:_:)) were called. The type encoding specified by `types` is ignored. --- 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)