RegisterCallbackHandler typedef Null safety

ZoneCallback<R> RegisterCallbackHandler <R>(
  1. Zone self,
  2. ZoneDelegate parent,
  3. Zone zone,
  4. R f(

    The type of a custom Zone.registerCallback implementation function.

    Receives the Zone that the handler was registered on as self, a delegate forwarding to the handlers of self's parent zone as parent, and the current zone where the error was uncaught as zone, which will have self as a parent zone.

    The function f is the function which was passed to the Zone.registerCallback of zone.

    The handler should return either the function f or another function replacing f, typically by wrapping f in a function which does something extra before and after invoking f


    typedef RegisterCallbackHandler = ZoneCallback<R> Function<R>(
        Zone self, ZoneDelegate parent, Zone zone, R Function() f);