Right-bias Either

- Add operations like map, flatMap which assume right-bias
- Deprecate {Left,Right}Projection
- Deprecate left and right in favor of swap
- Add contains, toOption, toTry, toSeq and filterOrElse
- toSeq returns collection.immutable.Seq instead of collection.Seq
- Don't add get

There are no incompatible changes.
The only possibility of breakage that exists is when people have added
extension methods named map, flatMap etc. to Either in the past doing
something different than the methods added to Either now.

One detail that moved the scales in favor of deprecating LeftProjection
and RightProjection was the desire to have toSeq return
scala.collection.immutable.Seq instead of scala.collection.Seq
like LeftProjection and RightProjection do.
Therefore keeping LeftProjection and RightProjection would introduce
inconsistency.

filter is called filterOrElse because filtering in a for-comprehension
doesn't work if the method needs an explicit argument.

contains was added as safer alternative to
  if (either.isRight && either.right.get == $something) ...

While adding filter with an implicit zero value is possible, it's
dangerous as it would require that developers add a "naked" implicit
value of type A to their scope and it would close the door to a future
in which the Scala standard library ships with Monoid and filter could
exist with an implicit Monoid parameter.

1 files changed, 2 insertions, 11 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/jvm/BackendReporting.scala b/src/compiler/scala/tools/nsc/backend/jvm/BackendReporting.scala
index 4287c24dc8..fd558587e9 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/BackendReporting.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/BackendReporting.scala
@@ -26,9 +26,7 @@ final class BackendReportingImpl(val global: Global) extends BackendReporting {
 /**
  * Utilities for error reporting.
  *
- * Defines some tools to make error reporting with Either easier. Would be subsumed by a right-biased
- * Either in the standard library (or scalaz \/) (Validation is different, it accumulates multiple
- * errors).
+ * Defines some utility methods to make error reporting with Either easier.
  */
 object BackendReporting {
   def methodSignature(classInternalName: InternalName, name: String, desc: String) = {
@@ -42,19 +40,12 @@ object BackendReporting {
   def assertionError(message: String): Nothing = throw new AssertionError(message)
 
   implicit class RightBiasedEither[A, B](val v: Either[A, B]) extends AnyVal {
-    def map[C](f: B => C): Either[A, C] = v.right.map(f)
-    def flatMap[C](f: B => Either[A, C]): Either[A, C] = v.right.flatMap(f)
     def withFilter(f: B => Boolean)(implicit empty: A): Either[A, B] = v match {
       case Left(_)  => v
       case Right(e) => if (f(e)) v else Left(empty) // scalaz.\/ requires an implicit Monoid m to get m.empty
     }
-    def foreach[U](f: B => U): Unit = v.right.foreach(f)
 
-    def getOrElse[C >: B](alt: => C): C = v.right.getOrElse(alt)
-
-    /**
-     * Get the value, fail with an assertion if this is an error.
-     */
+    /** Get the value, fail with an assertion if this is an error. */
     def get: B = {
       assert(v.isRight, v.left.get)
       v.right.get