Encapsulating data so the setter is private and getter is public

Question

I was wondering how it is best to create a data entity in C++, where the "setter" is private and "getter" is public. i.e the creator of the entity should be able to set the data, but the user/consumer/client is only able to get the data.

Lets consider the entity EntityX:

class EntityX
{
  public:
    EntityX(int x, int y) : x(x), y(y)
    {}
    int GetX() const {return x;}
    int GetY() const {return y;}
  private:
    int x,y; // Effective C++ third edition, Item 22: Declare data members private
}

And a class method which creates the entity and returns it to the client:

const shared_ptr<EntityX> classz::GetEntityX()
{
  shared_ptr<EntityX> entity(new EntityX(1,2));

  return entity;
}

This in my mind makes the setter private and the getter public, but this example is not practical if the data members are > 5-10... How would you make a entity class/struct such that the setter is "private" and the "getter" is "public", without making the constructor taking in all the data member variables.

Thanks in advance

Answer 1

What about setting your Creator as friend to class EntityX:

   class EntityX
    {
      friend class Creator;
      public:
        EntityX(int x, int y) : x(x), y(y)
        {}
        int GetX() const {return x;}
        int GetY() const {return y;}
      private:
        int x,y; // Effective C++ third edition, Item 22: Declare data members private
    };

---

Update:

Or you could use templatized friend-ship, see code below:

#include <iostream>
#include <memory>

template<class T>
class EntityX
  {
  friend T;
  public:
    EntityX(int x, int y) : x(x), y(y) {}
    int GetX() const {return x;}
    int GetY() const {return y;}
  private:
    int x,y; // Effective C++ third edition, Item 22: Declare data members private
  };

struct Creator
  {
    static const std::shared_ptr<EntityX<Creator>> create() 
      {  
      std::shared_ptr<EntityX<Creator>> entity = std::make_shared<EntityX<Creator>>(1,2);
      entity->x = 1;
      entity->y = 2;
      return entity;
      }
  };

int main()
{
  std::shared_ptr<EntityX<Creator>> const E = Creator::create();
  std::cout << E->GetX() << ", " << E->GetY() << std::endl;

  return 0 ; 
}