与其他模板化类中的所有模板化类成为朋友

Question

Look at following code:

template <typename T, int d>
class Grid {
   //Following line is what I need to change
   template<int d2> friend class Iterator<T,d,d2>;
}

template <typename T, int d, int d2>
class Iterator{ 
    //some code that use private fields of Grid<T,d>
}

template <typename T, int d>
class Iterator<T,d,0>{
    //This specialized class also need to use private parts of Grid<T,d>
}

Both specialized and not specialized Iterator should have access to private parts. Line:

template<int d2> friend class Iterator<T,d,d2>;

does not compile with error: partial specialization `Iterator' declared friend

Does anybody know how to replace it?

EDIT: Thanks to @Xeo comment i was able to make a workaround:

template<typename TT, int dd, int d2> friend class Iterator;

However this gives friend access to all Iterator templates not only to those one that have matching first and second template parameter.

Answer 1

这只是一种解决方法，但它可以正常工作：

template<typename TT, int dd, int d2> friend class Iterator;