---
title: "class_replaceMethod(_:_:_:_:)"
framework: Objective-C Runtime
role: symbol
role_heading: Function
platforms: [iOS 2.0+, iPadOS 2.0+, Mac Catalyst 13.1+, macOS 10.5+, tvOS 9.0+, visionOS 1.0+, watchOS 1.0+]
path: "objectivec/class_replacemethod(_:_:_:_:)"
---

# class_replaceMethod(_:_:_:_:)

Replaces the implementation of a method for a given class.

## Declaration

```swift
func class_replaceMethod(_ cls: AnyClass?, _ name: Selector, _ imp: IMP, _ types: UnsafePointer<CChar>?) -> 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 https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40008048 > 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

Return Value The previous implementation of the method identified by name for the class identified by cls.

## Discussion

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(_:_:_:_:) 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(_:_:) were called. The type encoding specified by types is ignored.

## See Also

### Working with Classes

- [class_getName(_:)](objectivec/class_getname(_:).md)
- [class_getSuperclass(_:)](objectivec/class_getsuperclass(_:).md)
- [class_setSuperclass(_:_:)](objectivec/class_setsuperclass(_:_:).md)
- [class_isMetaClass(_:)](objectivec/class_ismetaclass(_:).md)
- [class_getInstanceSize(_:)](objectivec/class_getinstancesize(_:).md)
- [class_getInstanceVariable(_:_:)](objectivec/class_getinstancevariable(_:_:).md)
- [class_getClassVariable(_:_:)](objectivec/class_getclassvariable(_:_:).md)
- [class_addIvar(_:_:_:_:_:)](objectivec/class_addivar(_:_:_:_:_:).md)
- [class_copyIvarList(_:_:)](objectivec/class_copyivarlist(_:_:).md)
- [class_getIvarLayout(_:)](objectivec/class_getivarlayout(_:).md)
- [class_setIvarLayout(_:_:)](objectivec/class_setivarlayout(_:_:).md)
- [class_getWeakIvarLayout(_:)](objectivec/class_getweakivarlayout(_:).md)
- [class_setWeakIvarLayout(_:_:)](objectivec/class_setweakivarlayout(_:_:).md)
- [class_getProperty(_:_:)](objectivec/class_getproperty(_:_:).md)
- [class_copyPropertyList(_:_:)](objectivec/class_copypropertylist(_:_:).md)