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copied!<p>There is a variant to create an empty mutable <code>Map</code> that has default values taken from the immutable <code>Map</code>. You may store a value and override the default at any time:</p> <pre><code>scala> import collection.immutable.{Map => IMap} //import collection.immutable.{Map=>IMap} scala> import collection.mutable.HashMap //import collection.mutable.HashMap scala> val iMap = IMap(1 -> "one", 2 -> "two") //iMap: scala.collection.immutable.Map[Int,java.lang.String] = Map((1,one), (2,two)) scala> val mMap = new HashMap[Int,String] { | override def default(key: Int): String = iMap(key) | } //mMap: scala.collection.mutable.HashMap[Int,String] = Map() scala> mMap(1) //res0: String = one scala> mMap(2) //res1: String = two scala> mMap(3) //java.util.NoSuchElementException: key not found: 3 // at scala.collection.MapLike$class.default(MapLike.scala:223) // at scala.collection.immutable.Map$Map2.default(Map.scala:110) // at scala.collection.MapLike$class.apply(MapLike.scala:134) // at scala.collection.immutable.Map$Map2.apply(Map.scala:110) // at $anon$1.default(<console>:9) // at $anon$1.default(<console>:8) // at scala.collection.MapLike$class.apply(MapLike.scala:134).... scala> mMap(2) = "three" scala> mMap(2) //res4: String = three </code></pre> <p><strong>Caveat</strong> (see the comment by Rex Kerr): You will not be able to remove the elements coming from the immutable map:</p> <pre><code>scala> mMap.remove(1) //res5: Option[String] = None scala> mMap(1) //res6: String = one </code></pre>

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