Function iterator

src/include/unordered_map_concurrent.h:108–115

        /// transfers the lock (if held) to this.  Caveat: the copied
        /// iterator no longer holds the lock!
        iterator (const iterator &src) {
            m_umc = src.m_umc;
            m_bin = src.m_bin;
            m_biniterator = src.m_biniterator;
            m_locked = src.m_locked;
            // assignment transfers lock ownership
            *(const_cast<bool *>(&src.m_locked)) = false;
        }

        /// Destroying an unordered_map_concurrent iterator releases any
        /// bin locks it held.