CODEWITHSUNDEEP
c++oopinner-classesencapsulation
trofchik
trofchik

Reputation: 87

How to encapsulate a class that is only being used inside another class?

Shown below is a rough structure of the program.

class Room 
{
private:
    Node* content;
public:
    void someRoomMethod();
};

void Room::someRoomMethod() {}


class Node
{
private:
    Node* nextNode;
    std::variant<int, float> data;
public:
    void someNodeMethod();
};

void Node::someNodeMethod() {}

As I mentioned in the title Node is not being used anywhere other than inside Room. I've tried to encapsulate Node by making it a nested class but it didn't work.

// Room.hh

class Room 
{
private:
    Room::Node* content; // ERROR: no type named "Node" in "Room" -- GCC

public:
    void roomMethod();

    class Node()
    {
    private:
        Node* nextNode;
        std::variant<int, float> data;
    public:
        void someNodeMethod();
    }
};

// Room.cpp
void Room::someRoomMethod() {} // sees Room in Room.hh

// Node.cpp
void Room::Node::someNodeMethod() {} // sees Node in Room.hh

Questions:

  1. How exactly should I encapsulate Node so that I could create a variable of type Node inside Room and so that Node couldn't be used anywhere except inside Room. Please note that I will need a linked list of type Node inside each instance Room.

  2. Should methods of Node be moved to external .cpp file like it is now? Is it a good practice?

Upvotes: 0

Views: 439

Answers (2)

cigien
cigien

Reputation: 60218

Declarations of a nested class are parsed lexically (the same as at file scope). Simply move the usage of Node after the definition:

class Room 
{  
  private:

    class Node
    {
      // ...
    };
  
    Room::Node* content; // fine, Node is defined already

  public:
     // ...
};

Since Node is only used inside Room it should be private.

Yes, you should move the definitions of Node methods to a .cpp file to separate implementation and interface. This is the same as for regular class methods.

Upvotes: 5

463035818_is_not_an_ai
463035818_is_not_an_ai

Reputation: 122450

You have to at least declare a type before you can use it:

class Room 
{


public:
    void roomMethod();

    class Node                          // no () 
    {
    private:
        Node* nextNode;
        std::variant<int, float> data;
    public:
        void someNodeMethod();
    };                                  // missing ;
private: 
    Node* content;

};

Upvotes: 1

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