<?php
/*
	I've discovered some slightly counter-intuitive behaviour
	with references and arrays. I'm not sure whether this is
	actually a bug or a 'feature', but if it is the latter then
	it should be documented as such.

	Consider the following code involving references and integers:
 */

$a = 5;
$b = &$a;
$c = $a;
$c = 10;

echo "(1) a: $a (should be 5)<br>\n";

/*
 	Here we have created a variable ($a), made a reference to it ($b),
	made a copy of the original variable ($c), changed the copy ($c=10),
	and then printed out the original value.
	
	This is all fine and as expected.

	Now let's try the same thing, but with the addition of arrays:
 */

$A = array();
$A[0] = 5;
$b = &$A[0];
$C = $A;
$C[0] = 10;

echo "(2) A[0]: $A[0] (I expected it to be 5)<br>\n";

/*
	Thus, having copied the array $A to $C, we have actually made
	$C[0] *another* reference to the $A[0] (which is also referenced
	by $c). I would have expected $C[0] to have become detached from
	the reference (as in $c = $a in the first example).
	
	Taking out the line '$b = &$A[0]' in the example above yields the
	expected behaviour:
 */

$A = array();
$A[0] = 5;
$C = $A;
$C[0] = 10;

echo "(3) A[0]: $A[0] (expected it to actually be 5 this time)<br>\n";

/*
	Q: What's the explanation for all of this?
	
	A: When the Zend Engine constructs a copy of an array/hash, it constructs
	copies of the individual elements by using zval_add_ref (zend_variables.c).
	This simply increases the reference count of the value in question. If
	that value happens to be referenced by more than one name, it has
	the 'is_ref' flag set. However, in the case of copying array elements,
	the values are still _not_ separated if they have 'is_ref' set.
	
	As I mentioned above, I'm not sure whether this is actually the desired
	behaviour or not. In either case, I couldn't find it documented clearly
	anywhere (maybe I didn't look hard enough--if not, sorry in advance!).
	
	Working under the assumption that the behaviour is incorrect (I 
	certainly find it very confusing), I worked out the following fix to
	the issue (assuming my understanding of the Zend Engine is correct):
	
		Instead of using zval_add_ref as the constructor when copying arrays,
		use this:
		
		ZEND_API void zval_add_ref_or_separate(zval **p)
		{
			if (PZVAL_IS_REF(*p))
			{
				SEPARATE_ZVAL(p);
			} else {
				zval_add_ref(p);
			}
		}
	
	Another question is whether there are similar issues with objects? I 
	haven't investigated...

	Note: I haven't included PHP modules/php.ini etc since I'm
fairly sure
	this issue is unrelated to any site-specific setup.
 */	
?>