Mine

<?php
	// Since people want to know why I double quote here it is.
	$key = -1;
	$array = array();
	$array[$key] = 'value';
	$key2 = -1.4567;
	$array[$key2] = 'value2';
	printr($array);
	function printr($array) {
		echo '<pre>';
		print_r($array);
		echo '</pre>';
	}
/*
Output:
<pre>Array
(
    [-1] => value2
)
</pre>
*/
	
?>