unset() side effects in functions

[Robert Enyedi <renyedi@xxxxxxxxx>]

I'm doing some experimenting with the unset() (http://php.net/unset) 
language construct in a PHP 5.2.1 installation. I did not find any 
documentation on what happens to an identically named local variable's 
value after an unset is performed.

Let me start with this example:

<?php
function dostuff() {
		$a = 4;
		echo ">in function (init): ".$a."<\n";
	
		global $a;
/*CHANGEME*/	unset($a);
	
		echo ">in function (after unset): ".$a."<\n";
		$a = 3;
		echo ">in function (after local assign): ".$a."<\n";
}

$a = 2;
dostuff();
echo ">in page: ".$a."<\n";
?>

The output is:
>in function (init): 4<
>in function (after unset): <
>in function (after local assign): 3<
>in page: 2<

So this basically means that the global $a is dereferenced by the 
unset() call and the local $a gets reinitialized.

A different thing happens when we replace the /*CHANGEME*/ line with 
unset using the $GLOBALS[] array (the recommended way of unsetting a 
global variable from inside a function):

unset($GLOBALS['a']);

This time the output is:

>in function (init): 4<
>in function (after unset): 2<
>in function (after local assign): 3<
>in page: <

Notice that after the unset statement the global $a is properly unset 
BUT the value of the local $a becomes 2, which was the value of the 
global $a at the function entry point.

Are these behaviors documented somewhere or should't I rely on these 
unset() side effects at all in my code?

Thanks,
Robert

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