PHP: File Extension Filter

fef.php

<?php
class FileExtensionFilter extends FilterIterator
{
    // whitelist of file extensions
    protected $ext = ["php", "txt"];

    // an abstract method which must be implemented in subclass
    public function accept() {
        return in_array($this->getExtension(), $this->ext);
    }
}

//create a new iterator
$dir = new FileExtensionFilter(new DirectoryIterator("./"));
...