Probably make quick_list destructor exclude all the elements.

[dmitriano]

It is not clear enough how its move assignment operator should work

    quick_list& operator = (quick_list&& other) noexcept
    {
        if (this != &other)
        {
            //quick_list cannot free its resources, so it is supposed to be empty
            assert(empty());
            attach(other);
        }
        return *this;
    }

Alternatively, it probably excludes its null element.