From 2e2373d9f3f9cb6997fc399b51237d20e15aad2b Mon Sep 17 00:00:00 2001
From: Sergei Semenov <sleepytomcat@gmail.com>
Date: Tue, 7 Dec 2021 07:48:57 -0800
Subject: [PATCH] Performance improvement for List::unfold, List::unfoldLeft
 (#2689)

---
 vavr/src/main/java/io/vavr/collection/List.java | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/vavr/src/main/java/io/vavr/collection/List.java b/vavr/src/main/java/io/vavr/collection/List.java
index 0c981ea9c..6442bb9e8 100644
--- a/vavr/src/main/java/io/vavr/collection/List.java
+++ b/vavr/src/main/java/io/vavr/collection/List.java
@@ -712,7 +712,8 @@ static <T, U> List<U> unfoldRight(T seed, Function<? super T, Option<Tuple2<? ex
      * @throws NullPointerException if {@code f} is null
      */
     static <T, U> List<U> unfoldLeft(T seed, Function<? super T, Option<Tuple2<? extends T, ? extends U>>> f) {
-        return Iterator.unfoldLeft(seed, f).toList();
+        return Iterator.unfoldRight(seed, f.andThen(tupleOpt -> tupleOpt.map(Tuple2::swap)))
+          .foldLeft(List.empty(), List::prepend);
     }
 
     /**
@@ -740,7 +741,8 @@ static <T, U> List<U> unfoldLeft(T seed, Function<? super T, Option<Tuple2<? ext
      * @throws NullPointerException if {@code f} is null
      */
     static <T> List<T> unfold(T seed, Function<? super T, Option<Tuple2<? extends T, ? extends T>>> f) {
-        return Iterator.unfold(seed, f).toList();
+        return Iterator.unfoldRight(seed, f.andThen(tupleOpt -> tupleOpt.map(Tuple2::swap)))
+          .foldLeft(List.empty(), List::prepend);
     }
 
     @Override