Error when calling function it self, VCS say="undefined function"

Question

I got this function from a question here. when I try on a separate file it runs normally. but when I rewrite it in a class that contains more functions I can rather call it in another file, the searchRec contained in this function (calling the function itself) turns red or is marked as an error by visual studio code. whereas before, above this function I also wrote the same function in which there is a function call itself, and it runs normally.

public function searchRec($haystack, $needle, $pathId=Array(), $pathIndex=Array())
{
    foreach($haystack as $index => $item) {
         
        $pathId[] = $item['Id'];
        $pathIndex[] = $index;
     
        if ($item['Title'] == $needle) {
    
            $returnObject = new stdClass();
             
            $returnObject->match = $item;   
            $returnObject->pathId = $pathId; 
            item directly
                $returnObject->pathIndex = $pathIndex; 
            return $returnObject;
        }
        
        if(isset($item['Children']) && count($item['Children']>0)) {
            (recursively) 
           
                $result = searchRec($item['Children'], $needle, $pathId, $pathIndex); //searchRec error, VCS says: undefined function
    
            if ($result) {
       
                return $result;
            }
        }
    }
    return false;
}

Answer 1

Since it's a class method, you need to call it with object-oriented syntax.

$result = $this->searchRec($item['Children'], $needle, $pathId, $pathIndex);