[SOLVED] & (by ref), not necessary?

[xtopolis]

I learned some OOP from a book, but it was PHP 4 style afaik.  Is this & necessary?

<?php
  $session = &new Session;
?>

 

or does it have the same effect as not having the & there, in PHP 5.2.x ?

 

And also, this means that it creates the same instance if it already exists?  or what?

[keeB]

Nope. It is no longer necessary as all variables are now passed by Reference.

 

The definition in Wikipedia:

In call-by-reference evaluation, a function receives an implicit reference to the argument, rather than a copy of its value. This means that the function can modify the argument, what will be seen by its caller. Call-by-reference therefore has the advantage of greater time- and space-efficiency (since arguments do not need to be copied), as well as the potential for greater communication between a function and its caller (since the function can return information using its reference arguments), but the disadvantage that a function must often take special steps to "protect" values it wishes to pass to other functions.

 

Edit:

 

To pass by value you must do the following (in PHP5)

 

<?php

class A{
   public $b = "hello";
}

$a = new A();
$b = $a;
$b->b = "hello from b";
echo $a->b; //prints "hello from b" because it was done by reference.

$c = clone $a;
$c->b = "hello from c";
echo $a->b; //prints "hello from b" because it was done by reference.
echo $c->b; //print "hello from c" because it was cloned.

 

 

[aschk]

Nope. It is no longer necessary as all variables are now passed by Reference.

 

Technically that's not correct, only object variables are passed as references NOT all variables. A string/boolean/int is passed by value as traditionally expected.

 

i.e.

$a = new A();  <- reference to object A

$b = $a    <- reference to object A

 

$c = 10;

$d = $b;  <- copy by value NOT a reference

[keeB]

Yeah, I was talking about in the context of OOP. I'll be more clear

[Xeoncross]

In PHP 5 the way references worked in OBJECTS switched.

"&" now points to the variable and NOT the variables reference.

 

<?php

class z {
    public $var = '';
}

//Objects by reference
$a = new z();
$b   =&  $a;
$c  = $a;

//Return values by reference
$var = $a->var;
$var2 =& $a->var;


//Change the value
foreach(array(null, 2) as $type) {

$a->var = $type;

print '<pre>';
var_dump($a, $b, $c, $var, $var2);
print '</pre><br />';
}


//Remove object ref
$a = null;

print '<pre>';
var_dump($a, $b, $c, $var, $var2);
print '</pre><br />';



?>

 

ouputs:

object(z)#1 (1) {
  ["var"]=>
  &NULL
}
object(z)#1 (1) {
  ["var"]=>
  &NULL
}
object(z)#1 (1) {
  ["var"]=>
  &NULL
}
string(0) ""
NULL


object(z)#1 (1) {
  ["var"]=>
  ∫(2)
}
object(z)#1 (1) {
  ["var"]=>
  ∫(2)
}
object(z)#1 (1) {
  ["var"]=>
  ∫(2)
}
string(0) ""
int(2)


NULL
NULL
object(z)#1 (1) {
  ["var"]=>
  ∫(2)
}
string(0) ""
int(2)