Diffrence between &new Object and new Object...

[kajaman (a.k.a. Hubert �ępicki ;))]

I must confess that I don't see the diffrence between using:

$MyObject = new Object();
and
$MyObject = &new Object();

Both expressions seem to produce new object and assign it to
$MyObject... Is there any reason to use "&new" instead of "new"?

[Steve]

There is no &new. The syntax is actually...

$MyObject =& new Object();

where =& is an assignment operator that creates a reference.

To see the difference, try this...

// example class
class MyClass
{
var $m_strValue;
function MyClass()
{
// initialise
$this->m_strValue = -1;
}
function SetValue( $p_strNewValue )
{
$this->m_strValue = $p_strNewValue;
}
function GetValue()
{
return $this->m_strValue;
}
}

$objMyObject1 = new MyClass();
print $objMyObject1->GetValue() . "\n";

// -1

$objMyObject1->SetValue(2);
print $objMyObject1->GetValue() . "\n";

// 2


$objMyObject2 =& new MyClass();
print $objMyObject1->GetValue() . "\n";

// 2 - would have been -1 if I hadn't created a reference!
See [url]http://www.php.net/manual/en/language.references.php[/url]

---
Steve

[kajaman (a.k.a. Hubert �ępicki ;))]

Steve wrote:

> There is no &new. The syntax is actually...
>
> $MyObject =& new Object();
>
> where =& is an assignment operator that creates a reference.
>
> To see the difference, try this...
>
> // example class
> class MyClass
> {
> var $m_strValue;
> function MyClass()
> {
> // initialise
> $this->m_strValue = -1;
> }
> function SetValue( $p_strNewValue )
> {
> $this->m_strValue = $p_strNewValue;
> }
> function GetValue()
> {
> return $this->m_strValue;
> }
> }
>
> $objMyObject1 = new MyClass();
> print $objMyObject1->GetValue() . "\n";
>
> // -1
>
> $objMyObject1->SetValue(2);
> print $objMyObject1->GetValue() . "\n";
>
> // 2
>
>
> $objMyObject2 =& new MyClass();
> print $objMyObject1->GetValue() . "\n";

[cut]
about the last line: shouldn't it be:
print $objMyObject2->GetValue(). "\n";
?

Ok, I will make some experiments, and I'll see how it works.

[kajaman (a.k.a. Hubert �ępicki ;))]

Ok, but I can't see any difference! It doesn't matter if I change = into
=& , printed values are the same!

I use PHP 5 - maybe this is the reason?

[Steve]

> about the last line: shouldn't it be:
> print $objMyObject2->GetValue(). "\n";

Oh dear. Yup, it should be. And, yup, when you correct that code
there's no difference between the two objects. Oh dear.

---
Steve

[Hilarion]

The difference is:

$MyObject = new Object();

does:
1. creates Object
2. makes a copy of it (not using the class standard constructor)
3. assigns the copy to $MyObject variable

$MyObject = & new Object();

does:
1. creates Object
2. assigns the object to $MyObject variable

Why? Cause "=" is a copying operator. When you use "= &" then you
get reference copied.


Example below shows the difference (you get "oryginal" objects in $instances array,
and copy in $instance variable). On PHP v 4.3.7 I get this result:

$instance_counter: 0

$instance = new MyClass();
$instance_counter: 1
$instance->name: default name
$instances[count($instances)-1]->name: default name
$instance->name = "some name";
$instance->name: some name
$instances[count($instances)-1]->name: default name

$instance = & new MyClass();
$instance_counter: 2
$instance->name: default name
$instances[count($instances)-1]->name: default name
$instance->name = "other name";
$instance->name: other name
$instances[count($instances)-1]->name: other name


Hilarion

<?php
$instance_counter = 0;
$instances = array();

class MyClass {
var $name;
function MyClass() {
global $instances, $instance_counter;
$this->name = 'default name';
$instances[] = &$this;
$instance_counter++;
}
}

echo '$instance_counter: ' . $instance_counter . "\r\n\r\n";

echo '$instance = new MyClass();'."\r\n";
$instance = new MyClass();

echo '$instance_counter: ' . $instance_counter . "\r\n";

echo '$instance->name: ' . $instance->name . "\r\n";
echo '$instances[count($instances)-1]->name: ' . $instances[count($instances)-1]->name . "\r\n";

echo '$instance->name = "some name";'."\r\n";
$instance->name = "some name";

echo '$instance->name: ' . $instance->name . "\r\n";
echo '$instances[count($instances)-1]->name: ' . $instances[count($instances)-1]->name . "\r\n\r\n";

echo '$instance = & new MyClass();'."\r\n";
$instance = & new MyClass();

echo '$instance_counter: ' . $instance_counter . "\r\n";

echo '$instance->name: ' . $instance->name . "\r\n";
echo '$instances[count($instances)-1]->name: ' . $instances[count($instances)-1]->name . "\r\n";

echo '$instance->name = "other name";'."\r\n";
$instance->name = "other name";

echo '$instance->name: ' . $instance->name . "\r\n";
echo '$instances[count($instances)-1]->name: ' . $instances[count($instances)-1]->name . "\r\n\r\n";
?>

[mmLiu]

My php version is Version 5.3.0,and the result is :


$instance_counter: 0



$instance = new MyClass();

$instance_counter: 1

$instance->name: default name

$instances[count($instances)-1]->name: default name

$instance->name = "some name";

$instance->name: some name

$instances[count($instances)-1]->name: some name



$instance = & new MyClass();

$instance_counter: 2

$instance->name: default name

$instances[count($instances)-1]->name: default name

$instance->name = "other name";

$instance->name: other name

$instances[count($instances)-1]->name: other name

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