From 04c40087c2013b3054b7d4e87e303fd8031fdfa5 Mon Sep 17 00:00:00 2001
From: Kacper Donat <kadet1090@gmail.com>
Date: Tue, 27 Oct 2026 22:18:48 +0100
Subject: [PATCH] hoist callback compilation out of transform closures

---
 src/Collections/transforms.php       | 51 ++++++++++++++++++----------
 tests/Collections/TransformsTest.php | 16 +++++++++
 2 files changed, 49 insertions(+), 18 deletions(-)

diff --git a/src/Collections/transforms.php b/src/Collections/transforms.php
index f84ba0e..52c94d5 100644
--- a/src/Collections/transforms.php
+++ b/src/Collections/transforms.php
@@ -44,9 +44,9 @@ use function Kadet\Functional\compile;
  */
 function map(callable $fn): \Closure
 {
-    return static function (iterable $input) use ($fn): iterable {
-        $fn = callback($fn);
+    $fn = callback($fn);
 
+    return static function (iterable $input) use ($fn): iterable {
         return keyedLike($input, (static function () use ($input, $fn) {
             foreach ($input as $key => $value) {
                 yield $key => $fn($value, $key);
@@ -69,9 +69,9 @@ function map(callable $fn): \Closure
  */
 function filter(?callable $fn = null): \Closure
 {
-    return static function (iterable $input) use ($fn): iterable {
-        $fn = $fn === null ? static fn ($value) => $value : callback($fn);
+    $fn = $fn === null ? static fn ($value) => $value : callback($fn);
 
+    return static function (iterable $input) use ($fn): iterable {
         return keyedLike($input, (static function () use ($input, $fn) {
             foreach ($input as $key => $value) {
                 if ($fn($value, $key)) {
@@ -94,10 +94,16 @@ function filter(?callable $fn = null): \Closure
  */
 function reject(callable $fn): \Closure
 {
-    return static function (iterable $input) use ($fn): iterable {
-        $fn = callback($fn);
+    $fn = callback($fn);
 
-        return filter(static fn ($value, $key) => !$fn($value, $key))($input);
+    return static function (iterable $input) use ($fn): iterable {
+        return keyedLike($input, (static function () use ($input, $fn) {
+            foreach ($input as $key => $value) {
+                if (!$fn($value, $key)) {
+                    yield $key => $value;
+                }
+            }
+        })());
     };
 }
 
@@ -116,9 +122,9 @@ function reject(callable $fn): \Closure
  */
 function flatMap(callable $fn): \Closure
 {
-    return static function (iterable $input) use ($fn): iterable {
-        $fn = callback($fn);
+    $fn = callback($fn);
 
+    return static function (iterable $input) use ($fn): iterable {
         return listLike($input, (static function () use ($input, $fn) {
             foreach ($input as $key => $value) {
                 $result = $fn($value, $key);
@@ -192,9 +198,10 @@ function unique(): \Closure
  */
 function uniqueBy(callable $selector): \Closure
 {
+    $selector = callback($selector);
+
     return static function (iterable $input) use ($selector): iterable {
-        $selector = callback($selector);
-        $seen     = seen();
+        $seen = seen();
 
         return keyedLike($input, (static function () use ($input, $selector, $seen) {
             foreach ($input as $key => $value) {
@@ -219,10 +226,10 @@ function uniqueBy(callable $selector): \Closure
  */
 function sort(?callable $comparator = null): \Closure
 {
-    return static function (iterable $input) use ($comparator): iterable {
-        // Comparators always take two values, so they are compiled without the ($value, $key) adaptation.
-        $comparator = $comparator === null ? static fn ($a, $b) => $a <=> $b : compile($comparator);
+    // Comparators always take two values, so they are compiled without the ($value, $key) adaptation.
+    $comparator = $comparator === null ? static fn ($a, $b) => $a <=> $b : compile($comparator);
 
+    return static function (iterable $input) use ($comparator): iterable {
         $entries = entries($input);
         usort($entries, static fn ($a, $b) => $comparator($a[1], $b[1]));
 
@@ -245,9 +252,9 @@ function sort(?callable $comparator = null): \Closure
  */
 function sortBy(callable $selector, bool $descending = false): \Closure
 {
-    return static function (iterable $input) use ($selector, $descending): iterable {
-        $selector = callback($selector);
+    $selector = callback($selector);
 
+    return static function (iterable $input) use ($selector, $descending): iterable {
         $entries = [];
         foreach ($input as $key => $value) {
             $entries[] = [$key, $value, $selector($value, $key)];
@@ -304,6 +311,10 @@ function slice(int $offset, ?int $length = null): \Closure
  */
 function take(int $n): \Closure
 {
+    if ($n < 0) {
+        throw new \InvalidArgumentException(sprintf('take(): count must be >= 0, got %d', $n));
+    }
+
     return slice(0, $n);
 }
 
@@ -314,6 +325,10 @@ function take(int $n): \Closure
  */
 function skip(int $n): \Closure
 {
+    if ($n < 0) {
+        throw new \InvalidArgumentException(sprintf('skip(): count must be >= 0, got %d', $n));
+    }
+
     return slice($n);
 }
 
@@ -400,9 +415,9 @@ function merge(iterable $other): \Closure
  */
 function each(callable $fn): \Closure
 {
-    return static function (iterable $input) use ($fn): iterable {
-        $fn = callback($fn);
+    $fn = callback($fn);
 
+    return static function (iterable $input) use ($fn): iterable {
         $reusable = is_array($input) || $input instanceof \Ds\Seq || $input instanceof \Ds\Map || $input instanceof \Ds\Set;
         if ($reusable) {
             foreach ($input as $key => $value) {
diff --git a/tests/Collections/TransformsTest.php b/tests/Collections/TransformsTest.php
index d701a01..1e47a65 100644
--- a/tests/Collections/TransformsTest.php
+++ b/tests/Collections/TransformsTest.php
@@ -300,6 +300,22 @@ class TransformsTest extends \PHPUnit\Framework\TestCase
         $this->assertSeq([2, 3], c\skip(1)(self::gen([1, 2, 3])));
     }
 
+    public function testTakeRejectsNegativeCount()
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('take(): count must be >= 0, got -1');
+
+        c\take(-1);
+    }
+
+    public function testSkipRejectsNegativeCount()
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('skip(): count must be >= 0, got -1');
+
+        c\skip(-1);
+    }
+
     // prepend / append / concat / merge
 
     public function testPrepend()