Smart Pointers & Move Semantics

#include <iostream>
#include <memory>
#include <vector>
using namespace std;

class Resource {
    string name;
public:
    Resource(const string &n) : name(n) { cout << name << " created\n"; }
    ~Resource() { cout << name << " destroyed\n"; }
    void use() const { cout << "Using " << name << endl; }
};

int main() {
    // unique_ptr: exclusive ownership (cannot be copied)
    auto res1 = make_unique<Resource>("FileHandle");
    res1->use();
    // auto res2 = res1;  // ERROR: cannot copy unique_ptr

    // Move ownership
    auto res2 = move(res1);  // res1 is now nullptr
    res2->use();
    // res1 is automatically deleted when scope ends

    // shared_ptr: shared ownership (reference counted)
    auto shared1 = make_shared<Resource>("DBConnection");
    {
        auto shared2 = shared1;  // Copy OK, ref count = 2
        cout << "Ref count: " << shared1.use_count() << endl; // 2
        shared2->use();
    }  // shared2 destroyed, ref count = 1
    cout << "Ref count: " << shared1.use_count() << endl; // 1
    // Resource destroyed when last shared_ptr goes out of scope

    // weak_ptr: non-owning reference (breaks cycles)
    weak_ptr<Resource> weak = shared1;
    if (auto locked = weak.lock()) {
        locked->use();  // Safe access
    }

    // Move semantics (efficient resource transfer)
    vector<string> v1 = {"hello", "world"};
    vector<string> v2 = move(v1);  // v1's data transferred to v2
    // v1 is now empty — no copy, just pointer swap!

    // Rule of 5: if you define any of: destructor, copy constructor,
    // copy assignment, move constructor, move assignment — define all 5

    return 0;
}