Inserted by the compiler when a mutation is detected during a foreach iteration.
- iOS 2.0+
- macOS 10.5+
- tvOS 9.0+
- watchOS 1.0+
The object being mutated.
The compiler inserts this function when it detects that an object is mutated during a foreach iteration. The function is called when a mutation occurs, and the enumeration mutation handler is enacted if it is set up (via the
objc_set function). If the handler is not set up, a fatal error occurs.