Instead of

```
class G1CardSetArray : public G1CardSetContainer {

  template<typename Derived>
  static size_t header_size_in_bytes_internal() {
    return offset_of(Derived, _data);
  }
  
  ...
  
  static size_t header_size_in_bytes() { return header_size_in_bytes_internal<G1CardSetArray>(); }

}
```

one can call `offset_of` directly on calculating the header size. The same pattern exists in other subclasses.