Merge pull request #152 from xuwei-k/Factory-type

Make `Factory` a transparent type alias to `CanBuildFrom`, in 2.11 and 2.12.

Author: julienrf

compat/src/main/scala-2.11_2.12/scala/collection/compat/PackageShared.scala

@@ -16,7 +16,7 @@ private[compat] trait PackageShared {
    * @tparam A Type of elements (e.g. `Int`, `Boolean`, etc.)
    * @tparam C Type of collection (e.g. `List[Int]`, `TreeMap[Int, String]`, etc.)
    */
-  type Factory[-A, +C] <: CanBuildFrom[Nothing, A, C] // Ideally, this would be an opaque type
+  type Factory[-A, +C] = CanBuildFrom[Nothing, A, C]
 
   implicit class FactoryOps[-A, +C](private val factory: Factory[A, C]) {
 
@@ -32,13 +32,6 @@ private[compat] trait PackageShared {
     def newBuilder: m.Builder[A, C] = factory()
   }
 
-  implicit def fromCanBuildFrom[A, C](implicit cbf: CanBuildFrom[Nothing, A, C]): Factory[A, C] =
-    cbf.asInstanceOf[Factory[A, C]]
-
-  implicit def fromCanBuildFromConversion[X, A, C](x: X)(
-      implicit toCanBuildFrom: X => CanBuildFrom[Nothing, A, C]): Factory[A, C] =
-    fromCanBuildFrom(toCanBuildFrom(x))
-
   implicit def genericCompanionToCBF[A, CC[X] <: GenTraversable[X]](
       fact: GenericCompanion[CC]): CanBuildFrom[Any, A, CC[A]] =
     simpleCBF(fact.newBuilder[A])

compat/src/test/scala/test/scala/collection/NoImportTest.scala

@@ -0,0 +1,16 @@
+package test.scala.collection
+
+// Don't import scala.collection.compat._
+import scala.collection.compat.Factory
+import scala.collection.{mutable, immutable}
+
+class NoImportTest {
+
+  implicitly[Factory[Int, List[Int]]]
+  implicitly[Factory[Char, String]]
+  implicitly[Factory[Char, Array[Char]]]
+  implicitly[Factory[Int, collection.BitSet]]
+  implicitly[Factory[Int, mutable.BitSet]]
+  implicitly[Factory[Int, immutable.BitSet]]
+
+}