fix: narrow minOf/maxOf return type

src/Collection.php

@@ -292,35 +292,39 @@ public function maxOrNull(?Closure $selector = null): mixed;
 	 * Returns the minimum value produced by the selector.
 	 * Throws if the collection is empty.
 	 *
-	 * @param Closure(E, int):mixed $selector
-	 * @return mixed
+	 * @template R of mixed
+	 * @param Closure(E, int):R $selector
+	 * @return R
 	 * @throws NoSuchElementException
 	 */
 	public function minOf(Closure $selector): mixed;
 
 	/**
 	 * Returns the minimum value produced by the selector, or null if empty.
 	 *
-	 * @param Closure(E, int):mixed $selector
-	 * @return mixed
+	 * @template R of mixed
+	 * @param Closure(E, int):R $selector
+	 * @return R|null
 	 */
 	public function minOfOrNull(Closure $selector): mixed;
 
 	/**
 	 * Returns the maximum value produced by the selector.
 	 * Throws if the collection is empty.
 	 *
-	 * @param Closure(E, int):mixed $selector
-	 * @return mixed
+	 * @template R of mixed
+	 * @param Closure(E, int):R $selector
+	 * @return R
 	 * @throws NoSuchElementException
 	 */
 	public function maxOf(Closure $selector): mixed;
 
 	/**
 	 * Returns the maximum value produced by the selector, or null if empty.
 	 *
-	 * @param Closure(E, int):mixed $selector
-	 * @return mixed
+	 * @template R of mixed
+	 * @param Closure(E, int):R $selector
+	 * @return R|null
 	 */
 	public function maxOfOrNull(Closure $selector): mixed;
 

tests/Type/MinMaxOfTypeTest.php

@@ -0,0 +1,27 @@
+<?php
+
+/**
+ * This file is part of the Noctud Collection.
+ * Copyright (c) Noctud.dev
+ */
+
+declare(strict_types=1);
+
+namespace Noctud\Collection\Tests\Type;
+
+use function Noctud\Collection\listOf;
+use function PHPStan\Testing\assertType;
+
+$strings = listOf(['a', 'bb']);
+
+// minOf/maxOf return the selector's type R instead of mixed.
+assertType('int', $strings->minOf(fn (string $s): int => (int) $s));
+assertType('int', $strings->maxOf(fn (string $s): int => (int) $s));
+assertType('float', $strings->maxOf(fn (string $s): float => (float) $s));
+
+// The OrNull variants add null for the empty-collection case.
+assertType('int|null', $strings->minOfOrNull(fn (string $s): int => (int) $s));
+assertType('int|null', $strings->maxOfOrNull(fn (string $s): int => (int) $s));
+
+// R is inferred even from an untyped selector parameter.
+assertType('int', listOf([1, 2, 3])->minOf(fn ($x) => (int) $x));