5. Which design pattern is used in the following code?

#include <string>

class AccountManager
{
private:
    AccountManager() { }
    AccountManager(const AccountManager&) = delete;
    AccountManager& operator=(const AccountManager&) = delete;

public:
    bool log_in(const std::string &user_name, const std::string &password);
    bool log_out(const std::string &user_name);
    bool sign_up(const std::string &user_name, const std::string &password,
                 const std::string &email);

public:
    static AccountManager& get_instance()
    {
        static AccountManager s;
        return s;
    }
};