fix: fix stream class syntax error

Author: inhere

src/Util/Optional.php

@@ -89,13 +89,14 @@ public static function ofNullable(mixed $value, mixed $nullValue = null): self
      */
     public static function ofArrayKey(ArrayAccess|array $array, int|string $key): self
     {
-        if (!(is_array($array) || $array instanceof ArrayAccess) || !isset($array[$key])) {
-            return self::empty();
-        }
-
-        return self::of($array[$key]);
+        return isset($array[$key]) ? self::of($array[$key]) : self::empty();
     }
 
+    /**
+     * @param callable(): mixed $fn
+     *
+     * @return static
+     */
     public static function ofReturn(callable $fn): self
     {
         return self::ofNullable($fn());
@@ -259,15 +260,18 @@ public function or(callable $supplier): self
      * If a value is present, returns a sequential Stream containing only that value,
      * otherwise returns an empty Stream.
      *
+     * @param class-string $streamClass
+     *
      * @return DataStream<T>
      */
-    public function stream(): DataStream
+    public function stream(string $streamClass = DataStream::class): DataStream
     {
+        /** @var $streamClass DataStream */
         if (!$this->isPresent()) {
-            return DataStream::empty();
+            return $streamClass::empty();
         }
 
-        return DataStream::of($this->value);
+        return $streamClass::of($this->value);
     }
 
     /**

src/Util/Stream/IntStream.php

@@ -11,12 +11,9 @@ class IntStream extends ListStream
 {
     /**
      * @param numeric $value
-     *
-     * @return $this
      */
-    public function append(mixed $value): static
+    public function append(mixed $value): void
     {
         parent::append((int)$value);
-        return $this;
     }
 }

src/Util/Stream/ListStream.php

@@ -9,14 +9,5 @@
  */
 class ListStream extends DataStream
 {
-    /**
-     * @param mixed $value
-     *
-     * @return $this
-     */
-    public function append(mixed $value): static
-    {
-        parent::append($value);
-        return $this;
-    }
+
 }

src/Util/Stream/StringStream.php

@@ -11,13 +11,10 @@ class StringStream extends ListStream
 {
     /**
      * @param mixed $value
-     *
-     * @return $this
      */
-    public function append(mixed $value): static
+    public function append(mixed $value): void
     {
         parent::append((string)$value);
-        return $this;
     }
 
     /**