inject.dart

List<dynamic> _stuff = [];

void inject(dynamic thing) {
  _stuff.add(thing);
}

T request<T>() => _stuff.firstWhere((thing) => thing is T, orElse: () => null);

class MyThing {
  final String value = 'hello, world';
}

void main() {
  inject(new MyThing());
  var thing = request<MyThing>();
  print(thing.value);
}