detach method Null safety

Detaches this finalizer from values attached with detach.

Each attachment between this finalizer and a value, which was created by calling attach with the detach object as detach argument, is removed.

If the finalizer was attached multiple times to the same value with different detachment keys, only those attachments which used detach are removed.

After detaching, an attachment won't cause any callbacks to happen if the object become inaccessible.

Example:

class Database {
  // Keeps the finalizer itself reachable, otherwise it might be disposed
  // before the finalizer callback gets a chance to run.
  static final Finalizer<DBConnection> _finalizer =
      Finalizer((connection) => connection.close());

  final DBConnection _connection;

  Database._fromConnection(this._connection);

  void close() {
    // User requested close.
    _connection.close();
    // Detach from finalizer, no longer needed.
    // Was attached using this object as `detach` token.
    _finalizer.detach(this);
  }

  // Some useful methods.
}