Make Eq contravariant

(and add it to commit set).

1 files changed, 17 insertions, 0 deletions

diff --git a/src/scala/Eq.scala b/src/scala/Eq.scala
new file mode 100644
index 000000000..697ec4318
--- /dev/null
+++ b/src/scala/Eq.scala
@@ -0,0 +1,17 @@
+package scala
+
+/** A marker class indicating that values of kind `T` can be compared. */
+class Eq[-L, -R]
+
+/** Besides being a companion object, this object
+ *  can also be used as a value that's compatible with
+ *  any instance of `Eq`.
+ */
+object Eq extends Eq[Any, Any] {
+
+  /** An implicit that provides an `Eq` instance for all types `T`
+   *  such that `T <: EqClass[T]`.
+   */
+  implicit def eqAny[L, R]: Eq[L, R] = Eq
+}
+