TaskMap: memoizes task-producing functions

tasks/standard/TaskMap.scala

@@ -0,0 +1,20 @@
+/* sbt -- Simple Build Tool
+ * Copyright 2010 Mark Harrah
+ */
+package sbt
+
+	import std._
+	import TaskExtra._
+	import collection.mutable
+
+object TaskMap
+{
+	/** Memoizes a function that produces a Task. */
+	def apply[A,B](f: A => Task[B]): A => Task[B] =
+	{
+		val map = new mutable.HashMap[A,Task[B]]
+		a => map.synchronized { map.getOrElseUpdate(a, f(a)) }
+	}
+	/** Lifts `f` to produce a Task and memoizes the lifted function. */
+	def make[A,B](f: A => B): A => Task[B] = apply( a => task(f(a)) )
+}