An approach for sane graphql-style fragment inheritence in dart https://dartpad.dartlang.org/ec9df3c1df23f415621fd3da7e81209e

graphql_fragments_in_dart.dart

// base type
class Foo {
  String _foo;
  int _bar;
}

//fragment exposing foo
class FooFragment extends Foo {
  String get foo => _foo;
  set foo(String value) => _foo = value;

  FooFragment({String foo}) {
    this.foo = foo;
  }
}

void main() {
  print(FooFragment(foo: 'foo').foo);
}