Связь объектов классов

#include <iostream>
#include <string>
#include <vector>
 
class Comment
{
public:
    Comment(const std::string &author, const std::string &content) 
        : m_author(author), m_content(content) {}
 
private:
    std::string m_author;
    std::string m_content;
    
    friend std::ostream &operator << (std::ostream &os, const Comment &comment)
    {
        std::cout << "Author: " << comment.m_author << '\n';
        std::cout << "Content: " << comment.m_content << '\n';
        
        return os;
    }
};
 
class Post
{
public:
    Post(const std::string &author, const std::string &title, const std::string &content)
        : m_author(author), m_title(title), m_content(content)
    {
    }
    
    void addComment(const Comment &comment)
    {
        m_comments.push_back(comment);
    }
private:
    std::string m_author;
    std::string m_title;
    std::string m_content;
    std::vector<Comment> m_comments;
    
    friend std::ostream &operator << (std::ostream &os, const Post &post)
    {
        std::cout << "=========POST=========\n";
        std::cout << "Author: " << post.m_author << '\n';
        std::cout << "Title: " << post.m_title << '\n';
        std::cout << "Content: " << post.m_content << '\n';
        std::cout << "=========POST END=========\n\n";
        
        std::cout << "=========POST COMMENTS=========\n";
        for (const Comment &comment : post.m_comments)
        {
            std::cout << comment;
            std::cout << "-=--=-=-=-=-=-=-=-=-=-\n";
        }
        std::cout << "=========POST COMMENTS END=========\n";
        
        return os;
    }
};
 
int main()
{
    Post post("Mike", "Post title", "Some question");
    post.addComment(Comment("John", "Comment1"));
    post.addComment(Comment("Vasya", "Comment2"));
    std::cout << post;
}

#include <vector>
 
class C
{
    
};
 
class B
{
    std::vector<C> value;
};
 
class A
{
    std::vector<B> value;
};