#include <cassert>
#include <memory>
#include <vector>
int main() {
    std::vector<int> original{1, 2};
    auto independent = original;
    independent[0] = 9;
    assert(original[0] == 1 && independent[0] == 9);
    std::weak_ptr<std::vector<int>> observer;
    {
        auto owner = std::make_shared<std::vector<int>>(original);
        observer = owner;
        {
            auto shared = owner;
            (*shared)[0] = 7;
            assert((*owner)[0] == 7);
        }
        auto pinned = observer.lock();
        assert(pinned && (*pinned)[0] == 7);
    }
    assert(observer.expired());
    assert(!observer.lock());
}