title: $set vs $addField in mongoDb Aggregation Framework
body: <p>With <strong>MongoDb 4.2</strong>, we have new aggregation stage <code>$set</code>. As per docs,</p>
  <blockquote>
  <p><code>$set</code> stage is an alias for <code>$addFields</code> (from mongoDb 3.4)</p>
  </blockquote>
  <p>But nothing mentioned why the need to have two stages with same functionality.</p>
  <p>Can someone help to understand this ? (possibly since versions &lt; 4.0 will be depricated soon )</p>