update comment for unreachable code and optimise sorted

typelevel · Mar 30, 2017 · 4709187 · 4709187
1 parent 22fd6b0
commit 4709187
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Showing 2 changed files with 12 additions and 4 deletions.
diff --git a/core/src/main/scala/cats/data/NonEmptyList.scala b/core/src/main/scala/cats/data/NonEmptyList.scala
@@ -231,12 +231,11 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
     * res0: cats.data.NonEmptyList[(Char, Int)] = NonEmptyList((z,1), (a,4), (e,22))
     * }}}
     */
-  def sortBy[B: Order](f: A => B): NonEmptyList[A] = {
+  def sortBy[B: Order](f: A => B): NonEmptyList[A] =
     toList.sortBy(f)(Order[B].toOrdering) match {
       case x :: xs => NonEmptyList(x, xs)
-      case Nil     => sys.error("absurd")
+      case Nil     => sys.error("unreachable: sorting a NonEmptyList cannot produce an empty List")
     }
-  }
 
   /**
     * Sorts this `NonEmptyList` according to an `Order`
@@ -250,7 +249,10 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
     * }}}
     */
   def sorted[AA >: A](implicit AA: Order[AA]): NonEmptyList[AA] =
-    sortBy(a => a: AA)
+    toList.sorted(Order[AA].toOrdering) match {
+      case x :: xs => NonEmptyList(x, xs)
+      case Nil     => sys.error("unreachable: sorting a NonEmptyList cannot produce an empty List")
+    }
 
   /**
     * Groups elements inside of this `NonEmptyList` using a mapping function

diff --git a/tests/src/test/scala/cats/tests/NonEmptyListTests.scala b/tests/src/test/scala/cats/tests/NonEmptyListTests.scala
@@ -244,6 +244,12 @@ class NonEmptyListTests extends CatsSuite {
     }
   }
 
+  test("NonEmptyList#sortBy is consistent with List#sortBy") {
+    forAll { (nel: NonEmptyList[Int], f: Int => Int) =>
+      nel.sortBy(f).toList should === (nel.toList.sortBy(f))
+    }
+  }
+
 
   test("NonEmptyList#groupBy is consistent with List#groupBy") {
     forAll { (nel: NonEmptyList[Int], f: Int => Int) =>