title: Is there an AddRange equivalent for a HashSet in C#
body: <p>With a list you can do:</p>
  <pre><code>list.AddRange(otherCollection);
  </code></pre>
  <p>There is no add range method in a <code>HashSet</code>.
  What is the best way to add another <code>ICollection</code> to a <code>HashSet</code>?</p>