description

# RegisterUnaryCallbackHandler typedef

RegisterUnaryCallbackHandler = ZoneUnaryCallback<R, T> Function<R, T>(Zone self, ZoneDelegate parent, Zone zone, R f(T arg))

The type of a custom Zone.registerUnaryCallback implementation function.

A function used as ZoneSpecification.registerUnaryCallback to specialize the behavior of a new zone.

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 which was passed to the Zone.registerUnaryCallback 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`

The function must only access zone-related functionality through `self`, `parent` or `zone`. It should not depend on the current zone (Zone.current).

## Implementation

    typedef RegisterUnaryCallbackHandler =
        ZoneUnaryCallback<R, T> Function<R, T>(
          Zone self,
          ZoneDelegate parent,
          Zone zone,
          R Function(T arg) f,
        );