Add a TriState value class.

Sometimes true and false aren't enough.

1 files changed, 26 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/util/TriState.scala b/src/reflect/scala/reflect/internal/util/TriState.scala
new file mode 100644
index 0000000000..c7a35d4637
--- /dev/null
+++ b/src/reflect/scala/reflect/internal/util/TriState.scala
@@ -0,0 +1,26 @@
+package scala
+package reflect
+package internal
+package util
+
+import TriState._
+
+/** A simple true/false/unknown value, for those days when
+ *  true and false don't quite partition the space.
+ */
+final class TriState private (val value: Int) extends AnyVal {
+  def isKnown = this != Unknown
+  def booleanValue = this match {
+    case True  => true
+    case False => false
+    case _     => sys.error("Not a Boolean value")
+  }
+}
+
+object TriState {
+  implicit def booleanToTriState(b: Boolean): TriState = if (b) True else False
+
+  val Unknown = new TriState(-1)
+  val False   = new TriState(0)
+  val True    = new TriState(1)
+}