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Optimize the foldM implementation for Vector #2552

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merged 1 commit into from Oct 4, 2018
Merged

Optimize the foldM implementation for Vector #2552

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12 changes: 12 additions & 0 deletions bench/src/main/scala/cats/bench/FoldBench.scala
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Expand Up @@ -3,13 +3,17 @@ package cats.bench
import cats.data.Const
import cats.instances.string._
import cats.instances.list._
import cats.instances.vector._
import cats.instances.option._
import cats.{Foldable, Traverse}
import org.openjdk.jmh.annotations.{Benchmark, Scope, State}

@State(Scope.Benchmark)
class FoldBench {

val chars: List[String] = ('a' to 'z').map(_.toString).toList
val charsVector: Vector[String] = chars.toVector
val combineStringsSome: (String, String) => Option[String] = (s1, s2) => Some(s1 + s2)

/** Benchmark fold of Foldable[List] */
@Benchmark
Expand All @@ -21,4 +25,12 @@ class FoldBench {
def traverseConst(): String =
Traverse[List].traverse[Const[String, ?], String, String](chars)(Const(_)).getConst

@Benchmark
def vectorToListFoldM(): Option[String] =
Foldable[List].foldM(charsVector.toList, "")(combineStringsSome)

@Benchmark
def vectorIndexFoldM(): Option[String] =
Foldable[Vector].foldM(charsVector, "")(combineStringsSome)

}
10 changes: 7 additions & 3 deletions core/src/main/scala/cats/instances/vector.scala
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Expand Up @@ -6,7 +6,6 @@ import cats.syntax.show._
import scala.annotation.tailrec
import scala.collection.+:
import scala.collection.immutable.VectorBuilder
import list._

trait VectorInstances extends cats.kernel.instances.VectorInstances {
implicit val catsStdInstancesForVector: Traverse[Vector] with Monad[Vector] with Alternative[Vector] with CoflatMap[Vector] =
Expand Down Expand Up @@ -89,8 +88,13 @@ trait VectorInstances extends cats.kernel.instances.VectorInstances {

override def isEmpty[A](fa: Vector[A]): Boolean = fa.isEmpty

override def foldM[G[_], A, B](fa: Vector[A], z: B)(f: (B, A) => G[B])(implicit G: Monad[G]): G[B] =
Foldable[List].foldM(fa.toList, z)(f)
override def foldM[G[_], A, B](fa: Vector[A], z: B)(f: (B, A) => G[B])(implicit G: Monad[G]): G[B] = {
val length = fa.length
G.tailRecM((z, 0)) { case (b, i) =>
if (i < length) G.map(f(b, fa(i)))(b => Left((b, i + 1)))
else G.pure(Right(b))
}
}

override def fold[A](fa: Vector[A])(implicit A: Monoid[A]): A = A.combineAll(fa)

Expand Down