gistfile1.php

<?php
function push_stack($stack, $idx, $val) {
	$val = array($idx => $val);//val is a zval*, the data its points to is already allocated on the heap, no duplication is needed
	$stack[] = $val;
	return $stack;
}

$stack = array();
$val = array('foo');

$stack = push_stack($stack, 7, $val);

var_dump($stack);