조금 더 강력하게 클래스 접근을 제한하는 방법.

---

Passkey Idiom

class Secure
{	
	int data;
	
public:
	static std::shared_ptr<Secure> CreateSecureObj(int data);
	class Key
	{
		friend std::shared_ptr<Secure> Secure::CreateSecureObj(int data);
		Key() {};
	};
	
	explicit Secure(const Key& key,  int data) : data{data} {};
};

std::shared_ptr<Secure> Secure::CreateSecureObj(int data)
{
	return std::make_shared<Secure>(Secure::Key(), data);
}

Usage

auto pSecure1 = Secure::CreateSecureObj(10); // OK
auto pSecure2 = std::make_shared<Secure>(Secure::Key(), 10); // Error
auto pSecure3 = new Secure(Secure::Key(), 10) // Error

Easy way in c++11

template <typename T>
class Key
{
	friend T;
	Key() {};
};

class Secure
{
	int data;
public:
	Secure(const Key<Secure>&, int data) : data{data} {};
	
	static std::shared_ptr<Secure> CreateSecureObj(int data);
};

std::shared_ptr<Secure> Secure::CreateSecureObj(int data)
{
	return std::make_shared<Secure>(Key<Secure>(), data);
}

Usage

auto pSecure1 = Secure::CreateSecureObj(10);  // OK
auto pSecure2 = std::make_shared<Secure>(Key<Secure>(), 10);  // Error
auto pSecure3 = new Secure(Key<Secure>(), 10);  // Error