NoSuchMethodError: Attempted to use type 'ThreesApp' as a function

[arden]

[VERBOSE-2:dart_error.cc(16)] Unhandled exception:
NoSuchMethodError: Attempted to use type 'ThreesApp' as a function. Since types do not define a method 'call', this is not possible. Did you intend to call the ThreesApp constructor and forget the 'new' operator?
Receiver: ThreesApp
Tried calling: ThreesApp()
#0 Object.noSuchMethod (dart:core-patch/dart:core/object_patch.dart:46)
#1 main (/Users/weibo/data/source/flutter/threes-flutter/lib/main.dart:9:32)
#2 _startIsolate. (dart:isolate-patch/dart:isolate/isolate_patch.dart:279)
#3 _RawReceivePortImpl._handleMessage (dart:isolate-patch/dart:isolate/isolate_patch.dart:165)

[diov]

因为用了 Dart 2 的语法，需要配置。
可以参考官方给的WIKI Trying the preview of Dart 2 in Flutter