runZoned<R> function Null safety

R runZoned<R>(
  1. R body(
      ),
    1. {Map<Object?, Object?>? zoneValues,
    2. ZoneSpecification? zoneSpecification,
    3. @Deprecated("Use runZonedGuarded instead") Function? onError}
    )

    Runs body in its own zone.

    Creates a new zone using Zone.fork based on zoneSpecification and zoneValues, then runs body in that zone and returns the result.

    Example use:

    var secret = "arglebargle"; // Or a random generated string.
var result = runZoned(
    () async {
      await Future.delayed(Duration(seconds: 5), () {
        print("${Zone.current[#_secret]} glop glyf");
      });
    },
    zoneValues: {#_secret: secret},
    zoneSpecification:
        ZoneSpecification(print: (Zone self, parent, zone, String value) {
      if (value.contains(Zone.current[#_secret] as String)) {
        value = "--censored--";
      }
      parent.print(zone, value);
    }));
secret = ""; // Erase the evidence.
await result; // Wait for asynchronous computation to complete.

    The new zone intercepts print and stores a value under the private symbol #_secret. The secret is available from the new Zone object, which is the Zone.current for the body, and is also the first, self, parameter to the print handler function.

    Implementation

    R runZoned<R>(R body(),
    {Map<Object?, Object?>? zoneValues,
    ZoneSpecification? zoneSpecification,
    @Deprecated("Use runZonedGuarded instead") Function? onError}) {
  checkNotNullable(body, "body");
  if (onError != null) {
    // TODO: Remove this when code have been migrated off using [onError].
    if (onError is! void Function(Object, StackTrace)) {
      if (onError is void Function(Object)) {
        var originalOnError = onError;
        onError = (Object error, StackTrace stack) => originalOnError(error);
      } else {
        throw ArgumentError.value(onError, "onError",
            "Must be Function(Object) or Function(Object, StackTrace)");
      }
    }
    return runZonedGuarded(body, onError,
        zoneSpecification: zoneSpecification, zoneValues: zoneValues) as R;
  }
  return _runZoned<R>(body, zoneValues, zoneSpecification);
}