$previousValue = $this->deferredUpdatesAddCallableUpdateCallback;
$this->deferredUpdatesAddCallableUpdateCallback = $callback;
return new ScopedCallback( function() use ( $previousValue ) {
$previousValue = $this->deferredUpdatesAddCallableUpdateCallback;
$this->deferredUpdatesAddCallableUpdateCallback = $callback;
return new ScopedCallback( function() use ( $previousValue ) {