title: What is the difference between Sink and Stream in Flutter?
body: <p>The Google I/O 2018 <a href="https://www.youtube.com/watch?v=RS36gBEp8OI&amp;t=1663s" rel="noreferrer">video</a> about Flutter explains how to use Dart streams to manage state in a Flutter application. The speaker talked about using <code>Sink</code> as input stream and <code>Stream</code> as output stream. What is the difference between <code>Sink</code> and <code>Stream</code>? I searched the documentation but it doesn't say too much thanks.</p>