#include <iostream>
#include <memory>

class Resource
{
public:  
    int value;
	Resource() { std::cout << "Resource acquired\n"; }
	~Resource() { std::cout << "Resource deleted\n"; }
    void use() { std::cout<<"Resource use; value "<<value<<"\n"; }
};
std::shared_ptr<Resource> test1()
{
    // allocate memory from the heap: 
    // std::shared_ptr<Resource> res(new Resource); // one way
	auto res = std::make_shared<Resource>(); // another way
    std::cout<<"test1() using Resource\n";
    res->use();
    res->value = 1;
    std::cout<<"about to exit test1()\n";
    return res;
}
void test2(std::shared_ptr<Resource> res)
{
    std::cout<<"test2() using Resource res\n";
    res->value = 2;
    res->use();
    std::cout<<"about to exit test2()\n";
}
void test3( Resource& res)
{
    std::cout<<"test3() using Resource res\n";
    res.value = 3; 
    res.use(); 
    std::cout<<"about to exit test3()\n";
}

int main()
{
    std::shared_ptr<Resource> shared_res2;
    {
        auto shared_res1 = test1();
        std::cout<<"returned from test1()\n";
        std::cout<<"shared_res1 use_count = "<<shared_res1.use_count()<<"\n";
        std::cout<<"copying shared resource\n";
        shared_res2 = shared_res1;
        std::cout<<"shared_res1 use_count = "<<shared_res1.use_count()<<"\n";
    } // pointer shared_res1 is not destroyed, because shared_res2 needs it   
    {
        test2(shared_res2);
        std::cout<<"returned from test2()\n";  
    } 
    std::cout<<"shared_res2 use_count = "<<shared_res2.use_count()<<"\n";
    test3(*shared_res2);
}