Why return all values in the directory rather than the changed value?

[cumirror]

hi,

i'm confused by the implement of WatchTree in etcd store.

in WatchTree, it returns all values in the directory like this:

		for {
			// Check if the watch was stopped by the caller
			select {
			case <-stopCh:
				return
			default:
			}

			_, err := watcher.Next(context.Background())

			if err != nil {
				return
			}

			list, err = s.List(directory, opts)
			if err != nil {
				return
			}

			watchCh <- list
		}

why not just return the changed item like this:

		for {
			// Check if the watch was stopped by the caller
			select {
			case <-stopCh:
				return
			default:
			}

			result, err := watcher.Next(context.Background())

			if err != nil {
				return
			}

			watchCh <- &store.KVPair{
				Key:       key,
				Value:     []byte(result.Node.Value),
				LastIndex: result.Node.ModifiedIndex,
			}
		}

if key A in directory is changed, just return A and it's value, other keys in directory it's not necessary to return.