1 files changed, 35 insertions, 0 deletions
diff --git a/main/moduledefs/src/Cacher.scala b/main/moduledefs/src/Cacher.scala
new file mode 100644
index 00000000..023f03be
--- /dev/null
+++ b/main/moduledefs/src/Cacher.scala
@@ -0,0 +1,35 @@
+package mill.moduledefs
+
+import scala.collection.mutable
+import scala.reflect.macros.blackbox.Context
+
+
+trait Cacher{
+  private[this] lazy val cacherLazyMap = mutable.Map.empty[sourcecode.Enclosing, Any]
+
+  protected[this] def cachedTarget[T](t: => T)
+                                     (implicit c: sourcecode.Enclosing): T = synchronized{
+    cacherLazyMap.getOrElseUpdate(c, t).asInstanceOf[T]
+  }
+}
+
+object Cacher{
+  def impl0[T: c.WeakTypeTag](c: Context)
+                                   (t: c.Expr[T]): c.Expr[T] = {
+    c.Expr[T](wrapCached[T](c)(t.tree))
+  }
+  def wrapCached[R: c.WeakTypeTag](c: Context)(t: c.Tree) = {
+
+    import c.universe._
+    val owner = c.internal.enclosingOwner
+    val ownerIsCacherClass =
+      owner.owner.isClass &&
+        owner.owner.asClass.baseClasses.exists(_.fullName == "mill.moduledefs.Cacher")
+
+    if (ownerIsCacherClass && owner.isMethod) q"this.cachedTarget[${weakTypeTag[R]}]($t)"
+    else c.abort(
+      c.enclosingPosition,
+      "T{} members must be defs defined in a Cacher class/trait/object body"
+    )
+  }
+}
+\ No newline at end of file