added example of compiler issue; unable to create 'size' and 'empty' properties on Collection<T> and java.util.Map<T> it seems? wonder if its a qualified name issue - qualified names don't seem to be allowed on extension properties - will raise an issue...

stdlib/ktSrc/JavaUtilMap.kt

@@ -0,0 +1,39 @@
+package std.util
+
+import java.util.*
+
+// Map APIs
+
+/** Returns the size of the map */
+/* TODO get redeclaration errors
+val Map<*,*>.size : Int
+    get() = size()
+*/
+
+/** Returns true if this map is empty */
+/* TODO get redeclaration errors
+val Map<*,*>.empty : Boolean
+    get() = isEmpty()
+*/
+
+/** Returns the value for the given key or returns the result of the defaultValue function if there was no entry for the given key */
+inline fun <K,V> java.util.Map<K,V>.getOrElse(key: K, defaultValue: ()-> V) : V {
+  val current = this.get(key)
+  if (current != null) {
+    return current
+  } else {
+    return defaultValue()
+  }
+}
+
+/** Returns the value for the given key or the result of the defaultValue function is put into the map for the given value and returned */
+inline fun <K,V> java.util.Map<K,V>.getOrElseUpdate(key: K, defaultValue: ()-> V) : V {
+  val current = this.get(key)
+  if (current != null) {
+    return current
+  } else {
+    val answer = defaultValue()
+    this.put(key, answer)
+    return answer
+  }
+}