Merge pull request #792 from jsuereth/fixup/from-repr

Split @milessabin HasRepr into IsTraversableOnce and IsTraversableLike t...

4 files changed, 82 insertions, 33 deletions

diff --git a/src/library/scala/collection/GenTraversableLike.scala b/src/library/scala/collection/GenTraversableLike.scala
index eaec7a2a76..0d51230623 100644
--- a/src/library/scala/collection/GenTraversableLike.scala
+++ b/src/library/scala/collection/GenTraversableLike.scala
@@ -411,12 +411,3 @@ trait GenTraversableLike[+A, +Repr] extends Any with GenTraversableOnce[A] with
   def stringPrefix: String
 
 }
-
-object GenTraversableLike {
-  /** Manufacture a conversion from collection representation type `Repr` to
-   *  its corresponding `GenTraversableLike` given an implicitly available
-   *  instance of `FromRepr[Repr]`.
-   *  @see [[scala.collection.generic.FromRepr]]
-   */
-  implicit def fromRepr[Repr](implicit fr : FromRepr[Repr]) = fr.hasElem
-}
diff --git a/src/library/scala/collection/generic/FromRepr.scala b/src/library/scala/collection/generic/IsTraversableLike.scala
index c08761332c..7288322903 100644
--- a/src/library/scala/collection/generic/FromRepr.scala
+++ b/src/library/scala/collection/generic/IsTraversableLike.scala
@@ -18,14 +18,12 @@ package generic
  *
  *  Example usage,
  * {{{
- *    import scala.collection.generic.{ CanBuildFrom, FromRepr, HasElem }
- *
- *    class FilterMapImpl[A, Repr](val r : Repr)(implicit hasElem : HasElem[Repr, A]) {
- *      def filterMap[B, That](f : A => Option[B])
- *        (implicit cbf : CanBuildFrom[Repr, B, That]) : That = r.flatMap(f(_).toSeq)
+ *    class FilterMapImpl[A, Repr](val r: GenTraversableLike[A, Repr]) {
+ *      final def filterMap[B, That](f: A => Option[B])(implicit cbf: CanBuildFrom[Repr, B, That]): That =
+ *        r.flatMap(f(_).toSeq)
  *    }
- *
- *    implicit def filterMap[Repr : FromRepr](r : Repr) = new FilterMapImpl(r)
+ *    implicit def filterMap[Repr, A](r: Repr)(implicit fr: IsTraversableOnce[Repr]): FilterMapImpl[fr.A,Repr] =
+ *      new FilterMapImpl(fr.conversion(r))
  *
  *    val l = List(1, 2, 3, 4, 5)
  *    List(1, 2, 3, 4, 5) filterMap (i => if(i % 2 == 0) Some(i) else None)
@@ -33,24 +31,28 @@ package generic
  * }}}
  *
  * @author Miles Sabin
+ * @author J. Suereth
  * @since 2.10
  */
-trait FromRepr[Repr] {
+trait IsTraversableLike[Repr] {
+  /** The type of elements we can traverse over. */
   type A
-  val hasElem: HasElem[Repr, A]
+  /** A conversion from the representation type `Repr` to a `GenTraversableLike[A,Repr]`. */
+  val conversion: Repr => GenTraversableLike[A, Repr]
 }
 
-object FromRepr {
+object IsTraversableLike {
   import language.higherKinds
 
-  implicit val stringFromRepr : FromRepr[String] { type A = Char } = new FromRepr[String] {
-    type A = Char
-    val hasElem = implicitly[HasElem[String, Char]]
-  }
+  implicit val stringRepr: IsTraversableLike[String] { type A = Char } =
+    new IsTraversableLike[String] {
+      type A = Char
+      val conversion = implicitly[String => GenTraversableLike[Char, String]]
+    }
 
-  implicit def genTraversableLikeFromRepr[C[_], A0]
-    (implicit hasElem0: HasElem[C[A0], A0]) : FromRepr[C[A0]] { type A = A0 } = new FromRepr[C[A0]] {
+  implicit def genTraversableLikeRepr[C[_], A0](implicit conv: C[A0] => GenTraversableLike[A0,C[A0]]): IsTraversableLike[C[A0]] { type A = A0 } = 
+    new IsTraversableLike[C[A0]] {
       type A = A0
-      val hasElem = hasElem0
+      val conversion = conv
     }
 }
diff --git a/src/library/scala/collection/generic/IsTraversableOnce.scala b/src/library/scala/collection/generic/IsTraversableOnce.scala
new file mode 100644
index 0000000000..b336553231
--- /dev/null
+++ b/src/library/scala/collection/generic/IsTraversableOnce.scala
@@ -0,0 +1,62 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2003-2012, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+package scala.collection
+package generic
+
+/** Type class witnessing that a collection representation type `Repr` has
+ *  elements of type `A` and has a conversion to `GenTraversableOnce[A]`.
+ *
+ *  This type enables simple enrichment of `GenTraversableOnce`s with extension
+ *  methods which can make full use of the mechanics of the Scala collections
+ *  framework in their implementation.
+ *
+ *  Example usage,
+ * {{{
+ *    class FilterMapImpl[A, Repr](val r: GenTraversableOnce[A]) {
+ *      final def filterMap[B, That](f: A => Option[B])(implicit cbf: CanBuildFrom[Repr, B, That]): That = {
+ *        val b = cbf()
+ *        for(e <- r.seq) f(e) foreach (b +=)
+ *        b.result
+ *      }
+ *    }
+ *    implicit def filterMap[Repr, A](r: Repr)(implicit fr: IsTraversableOnce[Repr]): FilterMapImpl[fr.A,Repr] =
+ *      new FilterMapImpl[fr.A, Repr](fr.conversion(r))
+ *
+ *    val l = List(1, 2, 3, 4, 5)
+ *    List(1, 2, 3, 4, 5) filterMap (i => if(i % 2 == 0) Some(i) else None)
+ *    // == List(2, 4)
+ * }}}
+ *
+ * @author Miles Sabin
+ * @author J. Suereth
+ * @since 2.10
+ */
+trait IsTraversableOnce[Repr] {
+  /** The type of elements we can traverse over. */
+  type A
+  /** A conversion from the representation type `Repr` to a `GenTraversableOnce[A]`. */
+  val conversion: Repr => GenTraversableOnce[A]
+}
+
+object IsTraversableOnce {
+  import language.higherKinds
+
+  implicit val stringRepr: IsTraversableOnce[String] { type A = Char } =
+    new IsTraversableOnce[String] {
+      type A = Char
+      val conversion = implicitly[String => GenTraversableOnce[Char]]
+    }
+
+  implicit def genTraversableLikeRepr[C[_], A0](implicit conv: C[A0] => GenTraversableOnce[A0]): IsTraversableOnce[C[A0]] { type A = A0 } = 
+    new IsTraversableOnce[C[A0]] {
+      type A = A0
+      val conversion = conv
+    }
+}
+
diff --git a/src/library/scala/collection/generic/package.scala b/src/library/scala/collection/generic/package.scala
index 85b9995f2e..6eecb5e3ff 100644
--- a/src/library/scala/collection/generic/package.scala
+++ b/src/library/scala/collection/generic/package.scala
@@ -6,12 +6,6 @@ import language.higherKinds
 package object generic {
   type CanBuild[-Elem, +To] = CanBuildFrom[Nothing, Elem, To]
 
-  /** The type of conversions from a collection representation type
-   *  `Repr` to its corresponding GenTraversableLike.
-   *  @see [[scala.collection.generic.FromRepr]]
-   */
-  type HasElem[Repr, A] = Repr => GenTraversableLike[A, Repr]
-
   @deprecated("use ClassTagTraversableFactory instead", "2.10.0")
   type ClassManifestTraversableFactory[CC[X] <: Traversable[X] with GenericClassManifestTraversableTemplate[X, CC]] = ClassTagTraversableFactory[CC]
 
@@ -20,4 +14,4 @@ package object generic {
 
   @deprecated("use GenericClassTagTraversableTemplate instead", "2.10.0")
   type GenericClassManifestTraversableTemplate[+A, +CC[X] <: Traversable[X]] = GenericClassTagTraversableTemplate[A, CC]
-}
\ No newline at end of file
+}