# class_addIvar(_:_:_:_:_:) Adds a new instance variable to a class. ``` func class_addIvar(_ cls: AnyClass?, _ name: UnsafePointer, _ size: Int, _ alignment: UInt8, _ types: UnsafePointer?) -> Bool ``` ## Return Value [`YES`](/documentation/ObjectiveC/YES) if the instance variable was added successfully, otherwise [`NO`](/documentation/ObjectiveC/NO) (for example, the class already contains an instance variable with that name). ## Discussion This function may only be called after [`objc_allocateClassPair(_:_:_:)`](/documentation/ObjectiveC/objc_allocateClassPair(_:_:_:)) and before [`objc_registerClassPair(_:)`](/documentation/ObjectiveC/objc_registerClassPair(_:)). Adding an instance variable to an existing class is not supported. The class must not be a metaclass. Adding an instance variable to a metaclass is not supported. The instance variable’s minimum alignment in bytes is `1<