code: func (c *Ctrie) casRoot(ov, nv *iNode) bool {
  	c.assertReadWrite()
  	return atomic.CompareAndSwapPointer(
  		(*unsafe.Pointer)(unsafe.Pointer(&c.root)), unsafe.Pointer(ov), unsafe.Pointer(nv))
  }
docs: // casRoot performs a CAS on the Ctrie root.