“Some concern has arisen about the suitability of object-oriented classes in LGPL’d software being inherited by non-(L)GPL code. Generally, these concerns are unfounded, and clarification is given on the official GNU website:

The LGPL contains no special provisions for inheritance, because none are needed. Inheritance creates derivative works in the same way as traditional linking, and the LGPL permits this type of derivative work in the same way as it permits ordinary function calls”