SeqAn uses a special kind of hierarchical structure that we call 'template argument subclassing', which means that different specializations of a given class template are specified by template arguments. For example, the array string String<char, Array<100> > is a subclass of String<char> in the sense that all functions and metafunctions which are applicable to String<char> can also be applied to String<char, Array<100> >, while it is possible to overload some functions especially for String<char, Array<100> >. The rules of C++ overload resolution guarantee that the compiler always applies the most specific variant out of all existing implementations when an algorithm or trait has been called. This approach resembles class derivation in standard object-oriented programming, but it is often faster, since it uses static instead of dynamic function binding.