readonly properties

Hi, As 8.1 adds readonly properties I wonder which build-in properties should be defined readonly. Currently I could find build-in readonly properties only on PDO and DOM. Very incomplete list where readonly properties could make sense: 1. Enum properties: enum Test:string {

    case TEST = 'test';

} $case = TEST::TEST; $refl = (new ReflectionObject($case))->getProperty('value'); var_dump($refl->isReadOnly());  // false var_dump($refl->isPublic());  // true $case->value = 'foo'; // Fatal error: Uncaught Error: Enum properties are immutable 2. DateInterval->days $interval = (new DateTime())->diff(new DateTime()); var_dump($interval->days); // 0 $refl = (new ReflectionObject($interval))->getProperty('days'); var_dump($refl->isReadOnly()); // false var_dump($refl->isPublic()); // true $interval->days = 2; var_dump($interval->days);  // 0 3. Exception properties Exception properties are protected but does it really make sense to be able to modify an exception property after initialization? I know this would be a BC break :( Thanks for all the excellent work - Can't wait for 8.1 :) Marc