pass by reference

Anon

Hi all,Im adopting OOP method in building a Community site package.Actually Im begining to have problem like object sharing.How may I be sure that when I pass an object through a method,the object does pass by reference instead of copying itself?Ya,we did this by using pointer in C,but Im quite confused with PHPs pointer-like feature.
To make the question clear,Im giong to explain further. I hava a class that manages all presentation job and instatiates a db connection object. Now,Id like other classes be able to share this connection object instead of replicate it.What am I supposed to do?Thanks.

Anon

I don't think objects are ever passed by copy. Why would PHP copy an object ? It's much more efficient to pass the pointer.

Anon

Good question. First, I assume that your concern with sharing the database connection object has to do with sharing the db connection itself. In that case, you might want to read up on persistent connections in the annotated manual (http://www.php.net/manual/features.persistent-connections.php).

Second, the db connection is stored in a single variable, so if you make that static, it doesn't really matter how the object is passed. (PHP classes can't have static members, but you can kludge it by using a global variable defined outside the class or by making it a static variable within a method.)

Third, if my original assumption is totally off or you still want to know how objects are passed, read the annotated manual on classes (http://www.php.net/manual/language.oop.php). According to one note, unless you explicitly pass the object by reference (using &) a copy will be created.

Finally, the manual section on references briefly explains the difference between a PHP reference and a C pointer.

HTH,
Beth

Anon

I've done a little test, seems you're right, objects are passed by copy :

class foo
{
var $bar;
}

$a=new foo;
$b=$a;

$a->bar="Hello";
print $a->bar; //Gives "Hello"
print $b->bar; //Gives nothing

I must confess I'm a bit surprised. I still don't understand why PHP works like this. It's slower, consumes more memory and is useless.

Anon

But it gives you the option of doing it either way. If you want to create a reference instead of a copy, just use $b=&$a;.

Anon

I don't think objects are ever passed by copy. Why would PHP copy an object ? It's much more efficient to pass the pointer.

$a new MyObject;
$b = $a;

You will observe that two copies of the object now exist and doing:

$a->myfield = "foo";
echo $b->myfield;

will yield different results.

I agree with your efficiency point; the other case for passing pointers if a "parent" object maintains a list (read: array) of "child" objects (and likewise a child can have a pointer to a parent. Not that this is working in my code at the moment!).

Anon

I must confess I'm a bit surprised. I still don't understand why PHP works like this. It's slower, consumes more memory and is useless.

Given my current problems with inadvertantly copied objects, it would be useful if the default with objects was to reference, rather than copy, and maybe something like:

$a = *$b;

to copy explicitly?

Just a thought.