Why can a reference reference multiple variables?

Question

The values that are printed are both 11 and 12. Why is this? And is there a way to remove the reference for the clone?

class A {
    public $z = 10;
}

$a1 = new A();

$z = &$a1->z;

$a2 = clone $a1;

$a1->z = 11;

var_dump($z);

$a2->z = 12;

var_dump($z);

@divix This is not a practical situation, but a simplified example. — user2180613, Dec 01 '15 at 13:05
try `$a2 = $a1` this should solve your simplified problem... — Lino, Dec 01 '15 at 13:09
possible duplicate of http://stackoverflow.com/questions/4123571/how-to-make-a-copy-of-an-object-without-reference — Victor Radu, Dec 01 '15 at 13:10

score 0 · Answer 1 · answered Dec 01 '15 at 14:50

Why is this?

A: When you are cloning you are also cloning the reference.

$z = &Ref to $a1->z [0x000F]

$a2-z = [0x000F]

$a1->z = 11; //[0x000F] = 11;

Since both class instances reference the same memory, when you change $z it changes the value of both classes.

The only way to derefernce that value would be to unset it.

unset($a2->z);
$a2->z = 12;

here's a full example.

class A {
    public $z = 10;
}

$a1 = new A();

$z = &$a1->z;

$a2 = clone $a1;

$a3 = clone $a2;

$a1->z = 11;

var_dump($z);

$a2->z = 12;

var_dump($z);

unset($a3->z);
$a3->z = 13;
var_dump($z);
var_dump($a3->z);

The output is

int(11)
int(12)
int(12) //$z
int(13) //$a3->z So $a3->z is now unlinked from the Unset

I hope this answers your question

Why can a reference reference multiple variables?

1 Answers1