code: func (c *Ctrie) Size() uint {
  	// TODO: The size operation can be optimized further by caching the size
  	// information in main nodes of a read-only Ctrie – this reduces the
  	// amortized complexity of the size operation to O(1) because the size
  	// computation is amortized across the update operations that occurred
  	// since the last snapshot.
  	size := uint(0)
  	for _ = range c.Iterator(nil) {
  		size++
  	}
  	return size
  }
docs: // Size returns the number of keys in the Ctrie.