title: Working with immutable HashMap in Scala
body: <p>I have an immutable HashMap and want to add/remove values from it. The <a href="http://www.scala-lang.org/api/current/index.html#scala.collection.mutable.HashMap" rel="nofollow">Scala api docs</a> say that I have to use <code>+=</code> and <code>-=</code> methods, but they don't work and I get the following error:</p>
  
  <pre><code>error: value += is not a member of scala.collection.immutable.HashMap
  </code></pre>
  
  <p>How do I add or remove values from a HashMap in Scala?</p>