Variable passing by reference in objects

[Anon]

The code:

<?

class foo {
var $bar;

function foo() {
        $GLOBALS["secondobject"] = &$this;

    if (!$this->bar)
        $this->bar = "Bleh bleh blah";
}

}

$firstobject = new foo();

$secondobject->bar .= " buh";
print "<hr><pre>";
var_dump($firstobject, "firstobject");
print "</pre><hr><pre>";
var_dump($secondobject, "secondobject");
print "</pre><hr>";

?>

Produces:

---

object(foo)(1) {
["bar"]=>
string(14) "Bleh bleh blah"
}
string(11) "firstobject"

---

object(foo)(1) {
["bar"]=>
string(18) "Bleh bleh blah buh"
}
string(12) "secondobject"

---

While the code:

<?

class foo {
var $bar;

function foo() {
        $GLOBALS["secondobject"] = &$this;

    if (!$this->bar)
        $this->bar = "Bleh bleh blah";
}

}

$firstobject = new foo();
$firstobject->foo();
$secondobject->bar .= " buh";
print "<hr><pre>";
var_dump($firstobject, "firstobject");
print "</pre><hr><pre>";
var_dump($secondobject, "secondobject");
print "</pre><hr>";

?>

produces:

---

object(foo)(1) {
["bar"]=>
string(18) "Bleh bleh blah buh"
}
string(11) "firstobject"

---

object(foo)(1) {
["bar"]=>
string(18) "Bleh bleh blah buh"
}
string(12) "secondobject"

---

Why doesn't the constructor get runned properly at object creation...

I have to call the constructor explicitly for the reference to get properly set up...

Is this a bug? Or is it a feature? 🙂

Does it have something to do about the object not beeing properly set up when the constructor is called the first time... so that the reference to $secondobject does not get the way I want it...

[neuromancer]

I have been told this was the intent, if you have ever used "extends" you will notice the same thing

class b extends a {
function b() {
printf("b constructor\n");
}
}
class a {
function a() {
printf("a constructor\n");
}
}
$test = new a;

[Anon]

Thanks for your answer!

I am aware of that... You have to manually call the contstructor of a superclass... or whatever it is called...

But that was not the case... the problem was a that in the constructor of the class (it is a single class, not an extension)

In the constructor of the class I make an attempt to assign the global value $secondclass a reference to the class itself with the following line:

$GLOBALS["secondobject"] = &$this;

(Passing by reference)

This should make the variable $secondobject identic to $firstobject after the line

$firstobject = new foo();

which should initialize the constructor. However this does not seem to be the case.
This only creates $secondobject as a duplicate of $firstobject...
For instance calling
$secondobject->bar .= "buhu";
does not append "buhu" to $firstobject->bar

But if I after creating the object with
$firstobject = new foo();
calls the constructor again with
$firstobject->foo();
then $secondobject seem to be a reference to $firstobject...
after that
$secondobject->bar .= "buhu";
appends "buhu" to $firstobject->bar...

It confuses the hell out of me....

So what I suspect is that passing &$this out of the constructor does not necessary make the desired effect...

[taxilian]

The reason for the phenomenon that you are experiencing is found in the PHP manual (or hidden, perhaps I should say... took me awhile to find it) under "What References Do". If you do something like this:

$a = new foo();
$b = $a;

$b will not be the same class as $a... it will be a copy. You probably new that. What most people (including myself, until recently) fail to put together, is that using:

$a = new foo();

does exactly the same thing. Since "new foo()" returns an object, it copies that object and assigns it to $a. Thus, "new foo()" (or "$this" from foo's constructor) and "$a" are different classes. You can get around this by creating foo with:

$a =& new foo();

and then $a will be the same object as $this was in the object's constructor.

I hope I explained that correctly... it's 5:30 in the morning, and I haven't gotten around to going to bed yet. you can find this probably better explained on PHP's site in the online manual:

http://www.php.net/manual/en/language.references.whatdo.php

it's good reading... I recomend it.

Cheers,

Richard