Storing php object's property in another object as a reference - php

Question

Is it possible to store a reference to an object's property (class member variable which holds a scalar data such as string or integer) within an object of a different class?
I am trying to have the following two echo statements produce identical results.
<?php
$x = new Type;
$x->name = 'abcd';
echo "x.name=" . $x->name . '<br/>';
echo "x.obj.name=" . $x->obj->value . '<br/>';
class Type
{
public $obj; //Instance of Property (Property class defined below)
public $name;
function __construct()
{
$this->obj = new Property($this->name);
}
}
class Property
{
public $value;
function __construct($v)
{
$this->value = $v;
}
}

Answer 1

$this->obj = new Property($this->name);
Is called at the time of object creation. Which is executed before the assignment.
i.e.
When you call $x = new Type;
The constructor is called and you try to copy 'name' which is empty by then
May be what you want it following, rather than passing the value, pass $this and keep the referance.
<?php
class Type
{
public $obj; //Instance of Property (Property class defined below)
public $name;
function __construct()
{
$this->obj = new Property($this);
}
}
class Property
{
public $value;
function __construct($ref)
{
$this->value = $ref;
}
}
$x = new Type;
$x->name = 'abcd';
echo "x.name=" . $x->name . '<br/>';
echo "x.obj.name=" . $x->obj->value->name . '<br/>';

Answer 2

You can pass the name value inside the constructor.
$x = new Type('abcd');
Without doing that, your constructor will not know what $this->name is yet. So we use it in the constructor and set the classes property before using it.
function __construct($p_name){
$this->name = $p_name;
$this->obj = new Property($this->name);
}
You could just as easily set the value after calling the constructor and then initialize the reference afterwards -
class Type {
public $obj;
public $name;
function setProperty(){
$this->obj = new Property($this->name);
}
}
$x = new Type;
$x->name = 'abcd';
$x->setProperty();
echo "x.name=" . $x->name;
echo "x.obj.name=" . $x->obj->value;

Answer 3

This is an old question but just to add to this.
You can have an object with methods and properties inside of another object..
Example
$obj1 = new class1();
$obj2 = new class2($obj1); // you just grabbed $obj1 and stuck it inside $obj2
Now you can use the stored object's methods like so:
$obj2->obj1->method_from_obj1();
or access the stored object's properties like so:
$obj2->obj1->property_of_obj1;
This is SUPER convenient if you instantiated an object of some API and want to use the API methods inside of your own object.

Answer 4

While at the time of answering this question is 9+ years old, I've encountered a similar issue today and found a way to do what's requested.
In short: you should use references. Here's a a working example (PHP 8):
<?php
class Source
{
public int $counter = 10;
}
class Consumer
{
public int $value = 0;
public function __construct(int &$value)
{
$this->value = &$value;
}
}
$source = new Source();
// Pass property of Source instance to the consumer.
$consumer = new Consumer($source->counter);
assert($consumer->value === 10);
// Changing value in the Source instance.
$source->counter = 15;
// ... and value in the consumer updated as well.
assert($consumer->value === 15);
exit;
So, the answer is yes, it is possible.