compile-safe-locator.dart

abstract class Locator {
  Resolver<T, Locator> resolve<T>() => Resolver(this);
}

class Resolver<T, L extends Locator> {
  Resolver(this._locator);

  final L _locator;
}

// TODO: write Locator3 ... Locator50 + their extension

class Locator1<T1> extends Locator {
  Locator1(this._first);

  final T1 _first;

  Resolver<Res, Locator1<T1>> resolve<Res>() => Resolver(this);
}

class Locator2<T1, T2> extends Locator {
  Locator2(this._first, this._second);

  final T1 _first;
  final T2 _second;

  @override
  Resolver<Res, Locator2<T1, T2>> resolve<Res>() => Resolver(this);
}

extension LocatorAdd on Locator {
  Locator1<T1> add<T1>(T1 value()) {
    return Locator1(value());
  }
}

extension Locator1Add<T1> on Locator1<T1> {
  Locator2<T1, T2> add<T2>(T2 value) {
    return Locator2(_first, value);
  }
}

extension Value1<Res> on Resolver<Res, Locator1<Res>> {
  Res get value => _locator._first;
}

extension Value2A<Res> on Resolver<Res, Locator2<Object, Res>> {
  Res get value => _locator._second;
}

extension Value2B<Res> on Resolver<Res, Locator2<Res, Object>> {
  Res get value => _locator._first;
}

void main() {
  final locator = Locator1<int>(42).add<double>(42.0);

  String value = locator.resolve<String>().value; // should not compile
  int value2 = locator.resolve<int>().value; // resolves to Value2A
  double value3 = locator.resolve().value; // resolves to Value2B
}