c++ - Can I make a class template a friend of another class template?

Question

So recently I am studying "Data structures algorithms and applications in C++". I encounter a code in which a class template is a friend of another class template. I am inexperienced with class templates.

template<class T> 
class ChainNode{
friend Chain<T>
private:
    T data;
    ChainNode<T> *link;
};

template<class T>
class Chain {
public:
    Chain() {first = 0;}
    ~Chain();
    bool IsEmpty() const { return first == 0; }
    int Length() const;
    bool Find(int k, T& x) const;
    int Search(const T& x) const;
    Chain& Delete(int k, T& x);
    Chain& Insert(int k, const T& x);
    void Output(std::ostream &out) const;
private:
    ChainNode<T> *first;
};

This is the original code form the book. I get the error:

chainList.hpp:7:9: error: 'Chain' does not name a type 7 | friend Chain;

If I change friend Chain<T> to friend class Chain<T>, I get the error:

chainList.hpp:7:15: error: 'Chain' is not a class template 7 | friend class Chain;

So my question is, how to make a class template a friend of another class template, or, is it impossible? Thanks!

question from:https://stackoverflow.com/questions/65867754/can-i-make-a-class-template-a-friend-of-another-class-template

Answer 1

Waitting for answers