removed foldRightDefer consistency with foldRight; will break BC with…

… it's addition.
typelevel · Mar 11, 2020 · 190981c · 190981c
1 parent 74eb85d
commit 190981c
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Showing 3 changed files with 4 additions and 12 deletions.
diff --git a/core/src/main/scala/cats/syntax/foldable.scala b/core/src/main/scala/cats/syntax/foldable.scala
@@ -332,6 +332,9 @@ final class FoldableOps0[F[_], A](private val fa: F[A]) extends AnyVal {
   def maximumByOption[B: Order](f: A => B)(implicit F: Foldable[F]): Option[A] =
     F.maximumOption(fa)(Order.by(f))
 
+  /**
+   * Implementers are responsible for ensuring they maintain consistency with foldRight; this is not checked by laws on Scala 2.11
+   */
   def foldRightDefer[G[_]: Defer, B](gb: G[B])(fn: (A, G[B]) => G[B])(implicit F: Foldable[F]): G[B] =
     Defer[G].defer(
       F.foldLeft(fa, (z: G[B]) => z)(

diff --git a/laws/src/main/scala/cats/laws/FoldableLaws.scala b/laws/src/main/scala/cats/laws/FoldableLaws.scala
@@ -47,16 +47,6 @@ trait FoldableLaws[F[_]] extends UnorderedFoldableLaws[F] {
   ): IsEq[B] =
     F.foldM[Id, A, B](fa, b)(f) <-> F.foldLeft(fa, b)(f)
 
-  def foldRightDeferConsistentWithFoldRight[A, B](
-    fa: F[A],
-    f: (B, A) => B
-  )(implicit
-    M: Monoid[B]): IsEq[B] = {
-    val g: (A, Eval[B]) => Eval[B] = (a, ea) => ea.map(f(_, a))
-
-    F.foldRight(fa, Later(M.empty))(g).value <-> fa.foldRightDefer(Later(M.empty): Eval[B])(g).value
-  }
-
   /**
    * `reduceLeftOption` consistent with `reduceLeftToOption`
    */

diff --git a/laws/src/main/scala/cats/laws/discipline/FoldableTests.scala b/laws/src/main/scala/cats/laws/discipline/FoldableTests.scala
@@ -42,8 +42,7 @@ trait FoldableTests[F[_]] extends UnorderedFoldableTests[F] {
       "takeWhile_ reference" -> forAll(laws.takeWhile_Ref[A] _),
       "dropWhile_ reference" -> forAll(laws.dropWhile_Ref[A] _),
       "collectFirstSome reference" -> forAll(laws.collectFirstSome_Ref[A, B] _),
-      "collectFirst reference" -> forAll(laws.collectFirst_Ref[A, B] _),
-      "foldRightDefer consistency" -> forAll(laws.foldRightDeferConsistentWithFoldRight[A, B] _)
+      "collectFirst reference" -> forAll(laws.collectFirst_Ref[A, B] _)
     )
 }