#include <iostream>
#include <future>
#include <mutex>


static std::once_flag inited;

class Singleton {
private:
    static Singleton *instance;

    Singleton(){}
public:
    static Singleton *getInstance(){
        std::call_once(inited,[](){
            instance=new Singleton();
        });
        return instance;
    }

};

Singleton* Singleton::instance=nullptr;

int main(){

    Singleton* p = Singleton::getInstance();
    Singleton* p2 = Singleton::getInstance();

    bool equal_memory_region = p==p2;
    std::cout << equal_memory_region << std::endl;
}