public List <TSource> ToList() => Enumerable.HashSetToList(new HashSet <TSource>(_source, _comparer));
public List <TSource> ToList() => Enumerable.HashSetToList(FillSet());
public List <TSource> ToList() => Enumerable.HashSetToList(new HashSet <TSource>(_source, _comparer));
public List <TSource> ToList() => Enumerable.HashSetToList(FillSet());