gsl::owner<T*> pri_pop() noexcept
{
if (head_ == nullptr)
{
return nullptr;
}
auto e = head_;
head_ = e->fetch_next();
if (head_ == nullptr)
{
ACTX_ASSERTS(e == tail_);
tail_ = nullptr;
}
return (gsl::owner<T*>)e;
}
const_iterator operator++(int) {const_iterator rt(*this); fetch_next(); return rt;}
const_iterator& operator++() {fetch_next(); return *this;}
