Constructs a new std::experimental::weak_ptr object that shares
ownership with an existing object and has the same pointer value.
weak_ptr(weak_ptr const& other) noexcept
Constructs a new std::experimental::weak_ptr object with the
same pointer value as other
which shares ownership with other.
other->use_count(),
remains unchanged..
p.use_count()==other.use_count()
and !p.owner_before(other) and !other.owner_before(p)
Nothing.
#include <experimental/atomic>