Fix most strong mode warnings.

lib/src/result/error.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 
 import '../result.dart';
 import 'value.dart';
 
 /// A result representing a thrown error.
-class ErrorResult implements Result {
+class ErrorResult<T> implements Result<T> {

[Lasse Reichstein Nielsen, 2016/03/29 21:53:59]

I really dislike adding <T> here - it's completely unnecessary since the class
doesn't use it for anything.

An ErrorResult is a Result<T> for any <T>, which is why it was declared as
Result<dynamic>. That's actually accurate - if you get an error from a
Future<int>, you should be able to make a Future<String> with the same error
without the error enforcing the type of the future unnecessarily.

[nweiz, 2016/03/30 00:57:18]

I understand the logic behind this being a Result<dynamic>, but it just doesn't
work with strong mode. In strong mode, Result<dynamic> is! Result<T> for any T
other than dynamic.

   final error;
   final StackTrace stackTrace;
 
   bool get isValue => false;
   bool get isError => true;
-  ValueResult get asValue => null;
-  ErrorResult get asError => this;
+  ValueResult<T> get asValue => null;
+  ErrorResult<T> get asError => this;
 
   ErrorResult(this.error, this.stackTrace);
 
   void complete(Completer completer) {
     completer.completeError(error, stackTrace);
   }
 
   void addTo(EventSink sink) {
     sink.addError(error, stackTrace);
   }
 
-  Future get asFuture => new Future.error(error, stackTrace);
+  Future<T> get asFuture => new Future.error(error, stackTrace);

[Lasse Reichstein Nielsen, 2016/03/29 21:53:59]

Should this be  new Future<T>.error ?
(Then, at least, the type is used for something).

[nweiz, 2016/03/30 00:57:18]

That's inferred via downward inference.

[Lasse Reichstein Nielsen, 2016/03/30 16:00:18]

That doesn't work in the VM or pure Dart.

This code should be Dart (non-strong-mode) compatible, and if the return type
says Future<T>, then it should return a Future<T>, which it doesn't as written.

[nweiz, 2016/03/30 19:11:54]

I'm not sure what you mean by "pure Dart", but this does work in the VM. In
checked mode, `Future<generic> is Future<T>`.

 
   /// Calls an error handler with the error and stacktrace.
   ///
   /// An async error handler function is either a function expecting two
   /// arguments, which will be called with the error and the stack trace, or it
   /// has to be a function expecting only one argument, which will be called
   /// with only the error.
   void handle(Function errorHandler) {
     if (errorHandler is ZoneBinaryCallback) {
       errorHandler(error, stackTrace);
     } else {
       errorHandler(error);
     }
   }
 }