From 702ab8b9d1ebad207bb7c97eb671da333e667ea0 Mon Sep 17 00:00:00 2001
From: Tim Spence <timothywspence@gmail.com>
Date: Tue, 19 Dec 2023 11:50:56 +0000
Subject: [PATCH] Vector-based optimized traverse and traverseFilter in the
 same commit for the sake of benchmarking

---
 core/src/main/scala/cats/Traverse.scala         | 4 ++--
 core/src/main/scala/cats/TraverseFilter.scala   | 4 ++--
 core/src/main/scala/cats/data/Chain.scala       | 6 +++---
 core/src/main/scala/cats/instances/vector.scala | 2 +-
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/core/src/main/scala/cats/Traverse.scala b/core/src/main/scala/cats/Traverse.scala
index cc2993ee69..f1856fdc53 100644
--- a/core/src/main/scala/cats/Traverse.scala
+++ b/core/src/main/scala/cats/Traverse.scala
@@ -288,8 +288,8 @@ object Traverse {
 
   private[cats] def traverseDirectly[G[_], A, B](
     fa: IterableOnce[A]
-  )(f: A => G[B])(implicit G: StackSafeMonad[G]): G[Chain[B]] = {
-    fa.iterator.foldLeft(G.pure(Chain.empty[B])) { case (accG, a) =>
+  )(f: A => G[B])(implicit G: StackSafeMonad[G]): G[Vector[B]] = {
+    fa.iterator.foldLeft(G.pure(Vector.empty[B])) { case (accG, a) =>
       G.map2(accG, f(a)) { case (acc, x) =>
         acc :+ x
       }
diff --git a/core/src/main/scala/cats/TraverseFilter.scala b/core/src/main/scala/cats/TraverseFilter.scala
index 0907ef3be7..25521b35f2 100644
--- a/core/src/main/scala/cats/TraverseFilter.scala
+++ b/core/src/main/scala/cats/TraverseFilter.scala
@@ -206,8 +206,8 @@ object TraverseFilter {
 
   private[cats] def traverseFilterDirectly[G[_], A, B](
     fa: IterableOnce[A]
-  )(f: A => G[Option[B]])(implicit G: StackSafeMonad[G]): G[Chain[B]] = {
-    fa.iterator.foldLeft(G.pure(Chain.empty[B])) { case (bldrG, a) =>
+  )(f: A => G[Option[B]])(implicit G: StackSafeMonad[G]): G[Vector[B]] = {
+    fa.iterator.foldLeft(G.pure(Vector.empty[B])) { case (bldrG, a) =>
       G.map2(bldrG, f(a)) {
         case (acc, Some(b)) => acc :+ b
         case (acc, None)    => acc
diff --git a/core/src/main/scala/cats/data/Chain.scala b/core/src/main/scala/cats/data/Chain.scala
index e113cae684..721cc66a50 100644
--- a/core/src/main/scala/cats/data/Chain.scala
+++ b/core/src/main/scala/cats/data/Chain.scala
@@ -1243,7 +1243,7 @@ sealed abstract private[data] class ChainInstances extends ChainInstances1 {
         else
           G match {
             case x: StackSafeMonad[G] =>
-              Traverse.traverseDirectly(fa.iterator)(f)(x)
+              x.map(Traverse.traverseDirectly(fa.iterator)(f)(x))(fromIterableOnce(_))
             case _ =>
               traverseViaChain {
                 val as = collection.mutable.ArrayBuffer[A]()
@@ -1355,7 +1355,7 @@ sealed abstract private[data] class ChainInstances extends ChainInstances1 {
     }
 
   implicit val catsDataTraverseFilterForChain: TraverseFilter[Chain] = new TraverseFilter[Chain] {
-    def traverse: Traverse[Chain] = Chain.catsDataInstancesForChain
+    def traverse: Traverse[Chain] with Alternative[Chain] = Chain.catsDataInstancesForChain
 
     override def filter[A](fa: Chain[A])(f: A => Boolean): Chain[A] = fa.filter(f)
 
@@ -1372,7 +1372,7 @@ sealed abstract private[data] class ChainInstances extends ChainInstances1 {
       else
         G match {
           case x: StackSafeMonad[G] =>
-            TraverseFilter.traverseFilterDirectly(fa.iterator)(f)(x)
+            x.map(TraverseFilter.traverseFilterDirectly(fa.iterator)(f)(x))(traverse.fromIterableOnce(_))
           case _ =>
             traverseFilterViaChain {
               val as = collection.mutable.ArrayBuffer[A]()
diff --git a/core/src/main/scala/cats/instances/vector.scala b/core/src/main/scala/cats/instances/vector.scala
index 06f93b4fef..b927ede1f1 100644
--- a/core/src/main/scala/cats/instances/vector.scala
+++ b/core/src/main/scala/cats/instances/vector.scala
@@ -271,7 +271,7 @@ private[instances] trait VectorInstancesBinCompat0 {
 
     def traverseFilter[G[_], A, B](fa: Vector[A])(f: (A) => G[Option[B]])(implicit G: Applicative[G]): G[Vector[B]] =
       G match {
-        case x: StackSafeMonad[G] => x.map(TraverseFilter.traverseFilterDirectly(fa)(f)(x))(_.toVector)
+        case x: StackSafeMonad[G] => TraverseFilter.traverseFilterDirectly(fa)(f)(x)
         case _ =>
           G.map(Chain.traverseFilterViaChain(fa)(f))(_.toVector)
       }