int main()
{
static_assert(( std::is_convertible<std::weak_ptr<A>, std::weak_ptr<B> >::value), "");
static_assert((!std::is_convertible<std::weak_ptr<B>, std::weak_ptr<A> >::value), "");
static_assert((!std::is_convertible<std::weak_ptr<A>, std::weak_ptr<C> >::value), "");
{
const std::weak_ptr<A> pA(std::shared_ptr<A>(new A));
assert(pA.use_count() == 0);
assert(B::count == 0);
assert(A::count == 0);
{
std::weak_ptr<B> pB(pA);
assert(B::count == 0);
assert(A::count == 0);
assert(pB.use_count() == 0);
assert(pA.use_count() == 0);
}
assert(pA.use_count() == 0);
assert(B::count == 0);
assert(A::count == 0);
}
assert(B::count == 0);
assert(A::count == 0);
{
std::weak_ptr<A> pA;
assert(pA.use_count() == 0);
assert(B::count == 0);
assert(A::count == 0);
{
std::weak_ptr<B> pB(pA);
assert(B::count == 0);
assert(A::count == 0);
assert(pB.use_count() == 0);
assert(pA.use_count() == 0);
}
assert(pA.use_count() == 0);
assert(B::count == 0);
assert(A::count == 0);
}
assert(B::count == 0);
assert(A::count == 0);
}
/* Notes *
* std::weak_ptr *
expired - checks whether the referenced object was already deleted
lock - creates a shared_ptr that manages the referenced object
* std::unique_ptr * ,using this instead of auto_ptr considering:
1 - operators supported(==, !=, < ...),so they can be used/stored in STL
which uses/relies on a lot of these operations
2 - array supported, can point to an array
*/
void f()
{
if ( !wp.expired()) {
auto spt = wp.lock();
std::cout << *spt << "\n";
std::cout << wp.use_count() << "\n";
}
else {
std::cout << "wp is expired\n";
}
}