PHP SplObjectStorage key() Function

<?php

// Create an empty SplObjectStorage
$str = new SplObjectStorage();

$obj = new StdClass;

$str->attach($obj, "d1");

$str->rewind();

// Get current index 
$index  = $str->key();

// Print Result
var_dump($index);
?>

<?php

// Create an Empty SplObjectStorage
$str = new SplObjectStorage();
 
$obj1 = new StdClass;
$obj2 = new StdClass;
$obj3 = new StdClass;
$obj4 = new StdClass;
 
$str->attach($obj1, "GeeksforGeeks");
$str->attach($obj2, "GFG");
$str->attach($obj3);
$str->attach($obj4, "DSA");
 
$str->rewind();
 
// Iterate and print data on each index
while($str->valid()) {
    
    // Get index 
    $index  = $str->key();
    $object = $str->current(); 
    $data   = $str->getInfo();
 
    var_dump($index, $data);
    $str->next();
}
?>