hierarchical in-memory settings

util/collection/Settings.scala

@@ -0,0 +1,29 @@
+package sbt
+
+sealed trait Settings
+{
+	def get[T](key: AttributeKey[T], path: List[String]): Option[T]
+	def set[T](key: AttributeKey[T], path: List[String], value: T): Settings
+}
+object Settings
+{
+	def empty: Settings = new Basic(Map.empty)
+	def x = 3
+
+	private[this] class Basic(val roots: Map[ List[String], AttributeMap ]) extends Settings
+	{
+		def get[T](key: AttributeKey[T], path: List[String]): Option[T] =
+		{
+			def notFound = path match {
+				case Nil => None
+				case x :: xs => get(key, xs)
+			}
+			(roots get path) flatMap ( _ get key ) orElse notFound
+		}
+		def set[T](key: AttributeKey[T], path: List[String], value: T): Settings =
+		{
+			val amap = (roots get path) getOrElse AttributeMap.empty
+			new Basic( roots updated(path, amap put(key, value)) )
+		}
+	}
+}