I have a library called Reactive-Dart that contains many composable operators for terminating and non-terminating sequences. For your scenario it would look something like this:

final newList = [];
Observable
   .fromList(['abc', 'abc', 'def'])
   .distinct()
   .observe((next) => newList.add(next), () => print(newList));

产生：

[abc, def]

我应该补充说，类似的功能。在github上检查一下，我相信你会找到一些合适的东西。

I should add that there are other libraries out there with similar features. Check around on github and I'm sure you'll find something suitable.