Make Zone API strong mode clean.

sdk/lib/async/zone.dart

Index: sdk/lib/async/zone.dart
diff --git a/sdk/lib/async/zone.dart b/sdk/lib/async/zone.dart
index 6ed22ec6d235b2e82a19ca38b14767b841f55cc0..c7f254e396c39d6083939a7d7197f99a08d64bb8 100644
--- a/sdk/lib/async/zone.dart
+++ b/sdk/lib/async/zone.dart
@@ -8,28 +8,21 @@ typedef R ZoneCallback<R>();
 typedef R ZoneUnaryCallback<R, T>(T arg);
 typedef R ZoneBinaryCallback<R, T1, T2>(T1 arg1, T2 arg2);
 
-// TODO(floitsch): we are abusing generic typedefs as typedefs for generic
-// functions.
-/*ABUSE*/
-typedef R HandleUncaughtErrorHandler<R>(
-    Zone self, ZoneDelegate parent, Zone zone, error, StackTrace stackTrace);
-/*ABUSE*/
-typedef R RunHandler<R>(Zone self, ZoneDelegate parent, Zone zone, R f());
-/*ABUSE*/
-typedef R RunUnaryHandler<R, T>(
-    Zone self, ZoneDelegate parent, Zone zone, R f(T arg), T arg);
-/*ABUSE*/
-typedef R RunBinaryHandler<R, T1, T2>(Zone self, ZoneDelegate parent, Zone zone,
-    R f(T1 arg1, T2 arg2), T1 arg1, T2 arg2);
-/*ABUSE*/
-typedef ZoneCallback<R> RegisterCallbackHandler<R>(
-    Zone self, ZoneDelegate parent, Zone zone, R f());
-/*ABUSE*/
-typedef ZoneUnaryCallback<R, T> RegisterUnaryCallbackHandler<R, T>(
-    Zone self, ZoneDelegate parent, Zone zone, R f(T arg));
-/*ABUSE*/
-typedef ZoneBinaryCallback<R, T1, T2> RegisterBinaryCallbackHandler<R, T1, T2>(
-    Zone self, ZoneDelegate parent, Zone zone, R f(T1 arg1, T2 arg2));
+typedef HandleUncaughtErrorHandler = void Function(Zone self,
+    ZoneDelegate parent, Zone zone, Object error, StackTrace stackTrace);
+typedef RunHandler = R Function<R>(
+    Zone self, ZoneDelegate parent, Zone zone, R Function() f);
+typedef RunUnaryHandler = R Function<R, T>(
+    Zone self, ZoneDelegate parent, Zone zone, R Function(T arg) f, T arg);
+typedef RunBinaryHandler = R Function<R, T1, T2>(Zone self, ZoneDelegate parent,
+    Zone zone, R Function(T1 arg1, T2 arg2) f, T1 arg1, T2 arg2);
+typedef RegisterCallbackHandler = ZoneCallback<R> Function<R>(
+    Zone self, ZoneDelegate parent, Zone zone, R Function() f);
+typedef RegisterUnaryCallbackHandler = ZoneUnaryCallback<R, T> Function<R, T>(
+    Zone self, ZoneDelegate parent, Zone zone, R Function(T arg) f);
+typedef RegisterBinaryCallbackHandler
+    = ZoneBinaryCallback<R, T1, T2> Function<R, T1, T2>(Zone self,
+        ZoneDelegate parent, Zone zone, R Function(T1 arg1, T2 arg2) f);
 typedef AsyncError ErrorCallbackHandler(Zone self, ZoneDelegate parent,
     Zone zone, Object error, StackTrace stackTrace);
 typedef void ScheduleMicrotaskHandler(
@@ -209,7 +202,7 @@ class _ZoneSpecification implements ZoneSpecification {
  *   to skip zones that would just delegate to their parents.
  */
 abstract class ZoneDelegate {
-  R handleUncaughtError<R>(Zone zone, error, StackTrace stackTrace);
+  void handleUncaughtError(Zone zone, error, StackTrace stackTrace);
   R run<R>(Zone zone, R f());
   R runUnary<R, T>(Zone zone, R f(T arg), T arg);
   R runBinary<R, T1, T2>(Zone zone, R f(T1 arg1, T2 arg2), T1 arg1, T2 arg2);
@@ -263,10 +256,14 @@ abstract class ZoneDelegate {
  * the protocol to be zone compatible.
  *
  * For convenience, zones provide [bindCallback] (and the corresponding
- * [bindUnaryCallback] or [bindBinaryCallback]) to make it easier to respect the
- * zone contract: these functions first invoke the corresponding `register`
+ * [bindUnaryCallback] and [bindBinaryCallback]) to make it easier to respect
+ * the zone contract: these functions first invoke the corresponding `register`
  * functions and then wrap the returned function so that it runs in the current
  * zone when it is later asynchronously invoked.
+ *
+ * Similarly, zones provide [bindCallbackGuarded] (and the corresponding
+ * [bindUnaryCallbackGuarded] and [bindBinaryCallbackGuarded]), when the
+ * callback should be invoked through [Zone.runGuarded].
  */
 abstract class Zone {
   // Private constructor so that it is not possible instantiate a Zone class.
@@ -312,7 +309,7 @@ abstract class Zone {
    * By default, when handled by the root zone, uncaught asynchronous errors are
    * treated like uncaught synchronous exceptions.
    */
-  R handleUncaughtError<R>(error, StackTrace stackTrace);
+  void handleUncaughtError(error, StackTrace stackTrace);
 
   /**
    * The parent zone of the this zone.
@@ -438,15 +435,15 @@ abstract class Zone {
    * This function is equivalent to:
    * ```
    * try {
-   *   return this.run(action);
+   *   this.run(action);
    * } catch (e, s) {
-   *   return this.handleUncaughtError(e, s);
+   *   this.handleUncaughtError(e, s);
    * }
    * ```
    *
    * See [run].
    */
-  R runGuarded<R>(R action());
+  void runGuarded(void action());
 
   /**
    * Executes the given [action] with [argument] in this zone and
@@ -454,7 +451,7 @@ abstract class Zone {
    *
    * See [runGuarded].
    */
-  R runUnaryGuarded<R, T>(R action(T argument), T argument);
+  void runUnaryGuarded<T>(void action(T argument), T argument);
 
   /**
    * Executes the given [action] with [argument1] and [argument2] in this
@@ -462,8 +459,8 @@ abstract class Zone {
    *
    * See [runGuarded].
    */
-  R runBinaryGuarded<R, T1, T2>(
-      R action(T1 argument1, T2 argument2), T1 argument1, T2 argument2);
+  void runBinaryGuarded<T1, T2>(
+      void action(T1 argument1, T2 argument2), T1 argument1, T2 argument2);
 
   /**
    * Registers the given callback in this zone.
@@ -501,37 +498,80 @@ abstract class Zone {
       R callback(T1 arg1, T2 arg2));
 
   /**
+   *  Registers the provided [callback] and returns a function that will
+   *  execute in this zone.
+   *
    *  Equivalent to:
    *
-   *      ZoneCallback registered = this.registerCallback(action);
-   *      if (runGuarded) return () => this.runGuarded(registered);
+   *      ZoneCallback registered = this.registerCallback(callback);
    *      return () => this.run(registered);
    *
    */
-  ZoneCallback<R> bindCallback<R>(R action(), {bool runGuarded: true});
+  ZoneCallback<R> bindCallback<R>(R callback());
 
   /**
+   *  Registers the provided [callback] and returns a function that will
+   *  execute in this zone.
+   *
    *  Equivalent to:
    *
-   *      ZoneCallback registered = this.registerUnaryCallback(action);
-   *      if (runGuarded) return (arg) => this.runUnaryGuarded(registered, arg);
+   *      ZoneCallback registered = this.registerUnaryCallback(callback);
    *      return (arg) => thin.runUnary(registered, arg);
    */
-  ZoneUnaryCallback<R, T> bindUnaryCallback<R, T>(R action(T argument),
-      {bool runGuarded: true});
+  ZoneUnaryCallback<R, T> bindUnaryCallback<R, T>(R callback(T argument));
 
   /**
+   *  Registers the provided [callback] and returns a function that will
+   *  execute in this zone.
+   *
    *  Equivalent to:
    *
-   *      ZoneCallback registered = registerBinaryCallback(action);
-   *      if (runGuarded) {
-   *        return (arg1, arg2) => this.runBinaryGuarded(registered, arg);
-   *      }
+   *      ZoneCallback registered = registerBinaryCallback(callback);
    *      return (arg1, arg2) => thin.runBinary(registered, arg1, arg2);
    */
   ZoneBinaryCallback<R, T1, T2> bindBinaryCallback<R, T1, T2>(
-      R action(T1 argument1, T2 argument2),
-      {bool runGuarded: true});
+      R callback(T1 argument1, T2 argument2));
+
+  /**
+   * Registers the provided [callback] and returns a function that will
+   * execute in this zone.
+   *
+   * When the function executes, errors are caught and treated as uncaught
+   * errors.
+   *
+   * Equivalent to:
+   *
+   *     ZoneCallback registered = this.registerCallback(callback);
+   *     return () => this.runGuarded(registered);
+   *
+   */
+  void Function() bindCallbackGuarded(void callback());
+
+  /**
+   * Registers the provided [callback] and returns a function that will
+   * execute in this zone.
+   *
+   * When the function executes, errors are caught and treated as uncaught
+   * errors.
+   *
+   * Equivalent to:
+   *
+   *     ZoneCallback registered = this.registerUnaryCallback(callback);
+   *     return (arg) => this.runUnaryGuarded(registered, arg);
+   */
+  void Function(T) bindUnaryCallbackGuarded<T>(void callback(T argument));
+
+  /**
+   *  Registers the provided [callback] and returns a function that will
+   *  execute in this zone.
+   *
+   *  Equivalent to:
+   *
+   *      ZoneCallback registered = registerBinaryCallback(callback);
+   *      return (arg1, arg2) => this.runBinaryGuarded(registered, arg1, arg2);
+   */
+  void Function(T1, T2) bindBinaryCallbackGuarded<T1, T2>(
+      void callback(T1 argument1, T2 argument2));
 
   /**
    * Intercepts errors when added programmatically to a `Future` or `Stream`.
@@ -565,16 +605,16 @@ abstract class Zone {
   AsyncError errorCallback(Object error, StackTrace stackTrace);
 
   /**
-   * Runs [action] asynchronously in this zone.
+   * Runs [callback] asynchronously in this zone.
    *
    * The global `scheduleMicrotask` delegates to the current zone's
    * [scheduleMicrotask]. The root zone's implementation interacts with the
    * underlying system to schedule the given callback as a microtask.
    *
    * Custom zones may intercept this operation (for example to wrap the given
-   * callback [action]).
+   * [callback]).
    */
-  void scheduleMicrotask(void action());
+  void scheduleMicrotask(void callback());
 
   /**
    * Creates a Timer where the callback is executed in this zone.
@@ -656,64 +696,47 @@ class _ZoneDelegate implements ZoneDelegate {
 
   _ZoneDelegate(this._delegationTarget);
 
-  R handleUncaughtError<R>(Zone zone, error, StackTrace stackTrace) {
+  void handleUncaughtError(Zone zone, error, StackTrace stackTrace) {
     var implementation = _delegationTarget._handleUncaughtError;
     _Zone implZone = implementation.zone;
     HandleUncaughtErrorHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implZone, _parentDelegate(implZone), zone, error, stackTrace)
-        as Object/*=R*/;
+    return handler(
+        implZone, _parentDelegate(implZone), zone, error, stackTrace);
   }
 
   R run<R>(Zone zone, R f()) {
     var implementation = _delegationTarget._run;
     _Zone implZone = implementation.zone;
     RunHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implZone, _parentDelegate(implZone), zone, f)
-        as Object/*=R*/;
+    return handler(implZone, _parentDelegate(implZone), zone, f);
   }
 
   R runUnary<R, T>(Zone zone, R f(T arg), T arg) {
     var implementation = _delegationTarget._runUnary;
     _Zone implZone = implementation.zone;
     RunUnaryHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R, T>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implZone, _parentDelegate(implZone), zone, f, arg)
-        as Object/*=R*/;
+    return handler(implZone, _parentDelegate(implZone), zone, f, arg);
   }
 
   R runBinary<R, T1, T2>(Zone zone, R f(T1 arg1, T2 arg2), T1 arg1, T2 arg2) {
     var implementation = _delegationTarget._runBinary;
     _Zone implZone = implementation.zone;
     RunBinaryHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R, T1, T2>' once
-    // it's supported. Remove the unnecessary cast.
-    return handler(implZone, _parentDelegate(implZone), zone, f, arg1, arg2)
-        as Object/*=R*/;
+    return handler(implZone, _parentDelegate(implZone), zone, f, arg1, arg2);
   }
 
   ZoneCallback<R> registerCallback<R>(Zone zone, R f()) {
     var implementation = _delegationTarget._registerCallback;
     _Zone implZone = implementation.zone;
     RegisterCallbackHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implZone, _parentDelegate(implZone), zone, f)
-        as Object/*=ZoneCallback<R>*/;
+    return handler(implZone, _parentDelegate(implZone), zone, f);
   }
 
   ZoneUnaryCallback<R, T> registerUnaryCallback<R, T>(Zone zone, R f(T arg)) {
     var implementation = _delegationTarget._registerUnaryCallback;
     _Zone implZone = implementation.zone;
     RegisterUnaryCallbackHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R, T>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implZone, _parentDelegate(implZone), zone, f)
-        as Object/*=ZoneUnaryCallback<R, T>*/;
+    return handler(implZone, _parentDelegate(implZone), zone, f);
   }
 
   ZoneBinaryCallback<R, T1, T2> registerBinaryCallback<R, T1, T2>(
@@ -721,10 +744,7 @@ class _ZoneDelegate implements ZoneDelegate {
     var implementation = _delegationTarget._registerBinaryCallback;
     _Zone implZone = implementation.zone;
     RegisterBinaryCallbackHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R, T1, T2>' once
-    // it's supported. Remove the unnecessary cast.
-    return handler(implZone, _parentDelegate(implZone), zone, f)
-        as Object/*=ZoneBinaryCallback<R, T1, T2>*/;
+    return handler(implZone, _parentDelegate(implZone), zone, f);
   }
 
   AsyncError errorCallback(Zone zone, Object error, StackTrace stackTrace) {
@@ -896,58 +916,60 @@ class _CustomZone extends _Zone {
    */
   Zone get errorZone => _handleUncaughtError.zone;
 
-  R runGuarded<R>(R f()) {
+  void runGuarded(void f()) {
     try {
-      return run(f);
+      run(f);
     } catch (e, s) {
-      return handleUncaughtError(e, s);
+      handleUncaughtError(e, s);
     }
   }
 
-  R runUnaryGuarded<R, T>(R f(T arg), T arg) {
+  void runUnaryGuarded<T>(void f(T arg), T arg) {
     try {
-      return runUnary(f, arg);
+      runUnary(f, arg);
     } catch (e, s) {
-      return handleUncaughtError(e, s);
+      handleUncaughtError(e, s);
     }
   }
 
-  R runBinaryGuarded<R, T1, T2>(R f(T1 arg1, T2 arg2), T1 arg1, T2 arg2) {
+  void runBinaryGuarded<T1, T2>(void f(T1 arg1, T2 arg2), T1 arg1, T2 arg2) {
     try {
-      return runBinary(f, arg1, arg2);
+      runBinary(f, arg1, arg2);
     } catch (e, s) {
-      return handleUncaughtError(e, s);
+      handleUncaughtError(e, s);
     }
   }
 
-  ZoneCallback<R> bindCallback<R>(R f(), {bool runGuarded: true}) {
+  ZoneCallback<R> bindCallback<R>(R f()) {
     var registered = registerCallback(f);
-    if (runGuarded) {
-      return () => this.runGuarded(registered);
-    } else {
-      return () => this.run(registered);
-    }
+    return () => this.run(registered);
   }
 
-  ZoneUnaryCallback<R, T> bindUnaryCallback<R, T>(R f(T arg),
-      {bool runGuarded: true}) {
+  ZoneUnaryCallback<R, T> bindUnaryCallback<R, T>(R f(T arg)) {
     var registered = registerUnaryCallback(f);
-    if (runGuarded) {
-      return (arg) => this.runUnaryGuarded(registered, arg);
-    } else {
-      return (arg) => this.runUnary(registered, arg);
-    }
+    return (arg) => this.runUnary(registered, arg);
   }
 
   ZoneBinaryCallback<R, T1, T2> bindBinaryCallback<R, T1, T2>(
-      R f(T1 arg1, T2 arg2),
-      {bool runGuarded: true}) {
+      R f(T1 arg1, T2 arg2)) {
     var registered = registerBinaryCallback(f);
-    if (runGuarded) {
-      return (arg1, arg2) => this.runBinaryGuarded(registered, arg1, arg2);
-    } else {
-      return (arg1, arg2) => this.runBinary(registered, arg1, arg2);
-    }
+    return (arg1, arg2) => this.runBinary(registered, arg1, arg2);
+  }
+
+  void Function() bindCallbackGuarded(void f()) {
+    var registered = registerCallback(f);
+    return () => this.runGuarded(registered);
+  }
+
+  void Function(T) bindUnaryCallbackGuarded<T>(void f(T arg)) {
+    var registered = registerUnaryCallback(f);
+    return (arg) => this.runUnaryGuarded(registered, arg);
+  }
+
+  void Function(T1, T2) bindBinaryCallbackGuarded<T1, T2>(
+      void f(T1 arg1, T2 arg2)) {
+    var registered = registerBinaryCallback(f);
+    return (arg1, arg2) => this.runBinaryGuarded(registered, arg1, arg2);
   }
 
   operator [](Object key) {
@@ -971,15 +993,13 @@ class _CustomZone extends _Zone {
 
   // Methods that can be customized by the zone specification.
 
-  R handleUncaughtError<R>(error, StackTrace stackTrace) {
+  void handleUncaughtError(error, StackTrace stackTrace) {
     var implementation = this._handleUncaughtError;
     assert(implementation != null);
     ZoneDelegate parentDelegate = _parentDelegate(implementation.zone);
     HandleUncaughtErrorHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implementation.zone, parentDelegate, this, error, stackTrace)
-        as Object/*=R*/;
+    return handler(
+        implementation.zone, parentDelegate, this, error, stackTrace);
   }
 
   Zone fork({ZoneSpecification specification, Map zoneValues}) {
@@ -996,10 +1016,7 @@ class _CustomZone extends _Zone {
     assert(implementation != null);
     ZoneDelegate parentDelegate = _parentDelegate(implementation.zone);
     RunHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implementation.zone, parentDelegate, this, f)
-        as Object/*=R*/;
+    return handler(implementation.zone, parentDelegate, this, f);
   }
 
   R runUnary<R, T>(R f(T arg), T arg) {
@@ -1007,10 +1024,7 @@ class _CustomZone extends _Zone {
     assert(implementation != null);
     ZoneDelegate parentDelegate = _parentDelegate(implementation.zone);
     RunUnaryHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R, T>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implementation.zone, parentDelegate, this, f, arg)
-        as Object/*=R*/;
+    return handler(implementation.zone, parentDelegate, this, f, arg);
   }
 
   R runBinary<R, T1, T2>(R f(T1 arg1, T2 arg2), T1 arg1, T2 arg2) {
@@ -1018,10 +1032,7 @@ class _CustomZone extends _Zone {
     assert(implementation != null);
     ZoneDelegate parentDelegate = _parentDelegate(implementation.zone);
     RunBinaryHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R, T1, T2>' once
-    // it's supported. Remove the unnecessary cast.
-    return handler(implementation.zone, parentDelegate, this, f, arg1, arg2)
-        as Object/*=R*/;
+    return handler(implementation.zone, parentDelegate, this, f, arg1, arg2);
   }
 
   ZoneCallback<R> registerCallback<R>(R callback()) {
@@ -1029,10 +1040,7 @@ class _CustomZone extends _Zone {
     assert(implementation != null);
     ZoneDelegate parentDelegate = _parentDelegate(implementation.zone);
     RegisterCallbackHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implementation.zone, parentDelegate, this, callback)
-        as Object/*=ZoneCallback<R>*/;
+    return handler(implementation.zone, parentDelegate, this, callback);
   }
 
   ZoneUnaryCallback<R, T> registerUnaryCallback<R, T>(R callback(T arg)) {
@@ -1040,10 +1048,7 @@ class _CustomZone extends _Zone {
     assert(implementation != null);
     ZoneDelegate parentDelegate = _parentDelegate(implementation.zone);
     RegisterUnaryCallbackHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R, T>' once it's
-    // supported. Remove the unnecessary cast.
-    return handler(implementation.zone, parentDelegate, this, callback)
-        as Object/*=ZoneUnaryCallback<R, T>*/;
+    return handler(implementation.zone, parentDelegate, this, callback);
   }
 
   ZoneBinaryCallback<R, T1, T2> registerBinaryCallback<R, T1, T2>(
@@ -1052,10 +1057,7 @@ class _CustomZone extends _Zone {
     assert(implementation != null);
     ZoneDelegate parentDelegate = _parentDelegate(implementation.zone);
     RegisterBinaryCallbackHandler handler = implementation.function;
-    // TODO(floitsch): make this a generic method call on '<R, T1, T2>' once
-    // it's supported. Remove the unnecessary cast.
-    return handler(implementation.zone, parentDelegate, this, callback)
-        as Object/*=ZoneBinaryCallback<R, T1, T2>*/;
+    return handler(implementation.zone, parentDelegate, this, callback);
   }
 
   AsyncError errorCallback(Object error, StackTrace stackTrace) {
@@ -1101,7 +1103,7 @@ class _CustomZone extends _Zone {
   }
 }
 
-R _rootHandleUncaughtError<R>(
+void _rootHandleUncaughtError(
     Zone self, ZoneDelegate parent, Zone zone, error, StackTrace stackTrace) {
   _schedulePriorityAsyncCallback(() {
     if (error == null) error = new NullThrownError();
@@ -1166,10 +1168,15 @@ AsyncError _rootErrorCallback(Zone self, ZoneDelegate parent, Zone zone,
         Object error, StackTrace stackTrace) =>
     null;
 
-void _rootScheduleMicrotask(Zone self, ZoneDelegate parent, Zone zone, f()) {
+void _rootScheduleMicrotask(
+    Zone self, ZoneDelegate parent, Zone zone, void f()) {
   if (!identical(_ROOT_ZONE, zone)) {
     bool hasErrorHandler = !_ROOT_ZONE.inSameErrorZone(zone);
-    f = zone.bindCallback(f, runGuarded: hasErrorHandler);
+    if (hasErrorHandler) {
+      f = zone.bindCallbackGuarded(f);
+    } else {
+      f = zone.bindCallback(f);
+    }
     // Use root zone as event zone if the function is already bound.
     zone = _ROOT_ZONE;
   }
@@ -1290,72 +1297,74 @@ class _RootZone extends _Zone {
 
   // Zone interface.
 
-  R runGuarded<R>(R f()) {
+  void runGuarded(void f()) {
     try {
       if (identical(_ROOT_ZONE, Zone._current)) {
-        return f();
+        f();
+        return;
       }
-      return _rootRun<R>(null, null, this, f);
+      _rootRun(null, null, this, f);
     } catch (e, s) {
-      return handleUncaughtError<R>(e, s);
+      handleUncaughtError(e, s);
     }
   }
 
-  R runUnaryGuarded<R, T>(R f(T arg), T arg) {
+  void runUnaryGuarded<T>(void f(T arg), T arg) {
     try {
       if (identical(_ROOT_ZONE, Zone._current)) {
-        return f(arg);
+        f(arg);
+        return;
       }
-      return _rootRunUnary<R, T>(null, null, this, f, arg);
+      _rootRunUnary(null, null, this, f, arg);
     } catch (e, s) {
-      return handleUncaughtError<R>(e, s);
+      handleUncaughtError(e, s);
     }
   }
 
-  R runBinaryGuarded<R, T1, T2>(R f(T1 arg1, T2 arg2), T1 arg1, T2 arg2) {
+  void runBinaryGuarded<T1, T2>(void f(T1 arg1, T2 arg2), T1 arg1, T2 arg2) {
     try {
       if (identical(_ROOT_ZONE, Zone._current)) {
-        return f(arg1, arg2);
+        f(arg1, arg2);
+        return;
       }
-      return _rootRunBinary<R, T1, T2>(null, null, this, f, arg1, arg2);
+      _rootRunBinary(null, null, this, f, arg1, arg2);
     } catch (e, s) {
-      return handleUncaughtError<R>(e, s);
+      handleUncaughtError(e, s);
     }
   }
 
-  ZoneCallback<R> bindCallback<R>(R f(), {bool runGuarded: true}) {
-    if (runGuarded) {
-      return () => this.runGuarded<R>(f);
-    } else {
-      return () => this.run<R>(f);
-    }
+  ZoneCallback<R> bindCallback<R>(R f()) {
+    return () => this.run<R>(f);
   }
 
-  ZoneUnaryCallback<R, T> bindUnaryCallback<R, T>(R f(T arg),
-      {bool runGuarded: true}) {
-    if (runGuarded) {
-      return (arg) => this.runUnaryGuarded<R, T>(f, arg);
-    } else {
-      return (arg) => this.runUnary<R, T>(f, arg);
-    }
+  ZoneUnaryCallback<R, T> bindUnaryCallback<R, T>(R f(T arg)) {
+    return (arg) => this.runUnary<R, T>(f, arg);
   }
 
   ZoneBinaryCallback<R, T1, T2> bindBinaryCallback<R, T1, T2>(
-      R f(T1 arg1, T2 arg2),
-      {bool runGuarded: true}) {
-    if (runGuarded) {
-      return (arg1, arg2) => this.runBinaryGuarded<R, T1, T2>(f, arg1, arg2);
-    } else {
-      return (arg1, arg2) => this.runBinary<R, T1, T2>(f, arg1, arg2);
-    }
+      R f(T1 arg1, T2 arg2)) {
+    return (arg1, arg2) => this.runBinary<R, T1, T2>(f, arg1, arg2);
+  }
+
+  void Function() bindCallbackGuarded(void f()) {
+    return () => this.runGuarded(f);
+  }
+
+  void Function(T) bindUnaryCallbackGuarded<T>(void f(T arg)) {
+    return (arg) => this.runUnaryGuarded(f, arg);
+  }
+
+  void Function(T1, T2) bindBinaryCallbackGuarded<T1, T2>(
+      void f(T1 arg1, T2 arg2)) {
+    return (arg1, arg2) => this.runBinaryGuarded(f, arg1, arg2);
   }
 
   operator [](Object key) => null;
 
   // Methods that can be customized by the zone specification.
 
-  R handleUncaughtError<R>(error, StackTrace stackTrace) {
-    return _rootHandleUncaughtError(null, null, this, error, stackTrace);
+  void handleUncaughtError(error, StackTrace stackTrace) {
+    _rootHandleUncaughtError(null, null, this, error, stackTrace);
   }
 
   Zone fork({ZoneSpecification specification, Map zoneValues}) {
@@ -1409,9 +1418,15 @@ const _ROOT_ZONE = const _RootZone();
 /**
  * Runs [body] in its own zone.
  *
+ * Returns the result of invoking [body].
+ *
  * If [onError] is non-null the zone is considered an error zone. All uncaught
  * errors, synchronous or asynchronous, in the zone are caught and handled
- * by the callback.
+ * by the callback. When the error is synchronous, throwing in the [onError]
+ * handler, leads to a synchronous exception.
+ *
+ * Returns `null` when [body] threw, and a provided [onError] function completed
+ * without throwing.
  *
  * Errors may never cross error-zone boundaries. This is intuitive for leaving
  * a zone, but it also applies for errors that would enter an error-zone.
@@ -1433,21 +1448,29 @@ const _ROOT_ZONE = const _RootZone();
  */
 R runZoned<R>(R body(),
     {Map zoneValues, ZoneSpecification zoneSpecification, Function onError}) {
+  // TODO(floitsch): the return type should be `void` here.
+  if (onError != null &&
+      onError is! ZoneBinaryCallback<Object, Object, StackTrace> &&
+      onError is! ZoneUnaryCallback<Object, Object>) {
+    throw new ArgumentError("onError callback must take an Object (the error), "
+        "or an Object (the error) and a StackTrace");
+  }
   HandleUncaughtErrorHandler errorHandler;
   if (onError != null) {
     errorHandler = (Zone self, ZoneDelegate parent, Zone zone, error,
         StackTrace stackTrace) {
       try {
-        // TODO(floitsch): the return type should be 'void'.
-        if (onError is ZoneBinaryCallback<dynamic, Object, StackTrace>) {
-          return self.parent.runBinary(onError, error, stackTrace);
+        if (onError is void Function(Object, StackTrace)) {
+          self.parent.runBinary(onError, error, stackTrace);
+          return;
         }
-        return self.parent.runUnary(onError, error);
+        assert(onError is void Function(Object));
+        self.parent.runUnary(onError, error);
       } catch (e, s) {
         if (identical(e, error)) {
-          return parent.handleUncaughtError(zone, error, stackTrace);
+          parent.handleUncaughtError(zone, error, stackTrace);
         } else {
-          return parent.handleUncaughtError(zone, e, s);
+          parent.handleUncaughtError(zone, e, s);
         }
       }
     };
@@ -1462,7 +1485,17 @@ R runZoned<R>(R body(),
   Zone zone = Zone.current
       .fork(specification: zoneSpecification, zoneValues: zoneValues);
   if (onError != null) {
-    return zone.runGuarded(body);
+    try {
+      return zone.run(body);
+    } catch (e, stackTrace) {
+      if (onError is ZoneBinaryCallback<R, Object, StackTrace>) {
+        zone.runBinary(onError, e, stackTrace);
+        return null;
+      }
+      assert(onError is ZoneUnaryCallback<R, Object>);
+      zone.runUnary(onError, e);
+      return null;
+    }
   } else {
     return zone.run(body);
   }