Sandbox::https://github.com/0voice/cpp_new_features/blob/main/cpp_11/003_stl_std_weak

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#include <iostream>

#include <memory>

void observe(std::weak_ptr<int> weak)

{

if (auto observe = weak.lock()) {

std::cout << "\tobserve() able to lock weak_ptr<>, value=" << *observe << "\n";

} else {

std::cout << "\tobserve() unable to lock weak_ptr<>\n";

}

int main()

{

std::weak_ptr<int> weak;

std::cout << "weak_ptr<> not yet initialized\n";

observe(weak);

{

auto shared = std::make_shared<int>(42);

weak = shared;

std::cout << "weak_ptr<> initialized with shared_ptr.\n";

observe(weak);

}

std::cout << "shared_ptr<> has been destructed due to scope exit.\n";

observe(weak);

}