(PHP5) Why does assignment work like cloning?

Question

PHP

Code from this page php.net/manual/ru/language.oop5.basic.php from example #4

<?php

$instance = new SimpleClass();

$assigned   =  $instance;
$reference  =& $instance;

$instance->var = '$assigned будет иметь это значение';

$instance = null; // $instance и $reference становятся null

var_dump($instance);
var_dump($reference);
var_dump($assigned);
?>

Result

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned будет иметь это значение"
}

And there is also cloning php.net/manual/en/language.oop5.cloning.php
I correctly understood that cloning without a __clone() method defined in the class does the same thing as a normal assignment? In general, I expected in this example that $assigned would be NULL, but in fact, as if they wrote $assigned = clone $instance;
So what's the difference?

Answer 1

There is no cloning magic here.
First, let's figure out what $instance stores. It stores the REFERENCE to the object and not the object itself. With a simple assignment by value, the value of the variable is copied, and we have it just a reference to an object. As a result, we already have two references to one object.
When assigning a value to the $reference variable by reference, we have two variables that share the same value. A value is a reference to an object.
When we overwrite the reference in $instance, that is, we change the value of it, it also changes in $reference, since they divide one value into two. $assigned has its own object reference.

$instance = new SimpleClass(); // количество ссылок на экземпляр SimpleClass - 1

$assigned   =  $instance; // количество ссылок на экземпляр SimpleClass - 2
$reference  =& $instance; // количество ссылок на экземпляр SimpleClass - 2

$instance = null; // количество ссылок на экземпляр SimpleClass - 1

As soon as we have no references to an instance of the class, the garbage collector will remove the object.
And as for the clone - if objects were copied, hell would begin, since objects store other objects that can be shared between other objects ... in a word, everything becomes too complicated there, and it’s better for the programmer to resolve it in __clone himself.

Answer 2

Read the php.net/manual/en/language.operators.assignment.php
documentation for the difference
Assignment Operators
...
Note that the assignment copies the original variable to the new one (assignment by value), so changes to one will not affect the other. This may also have relevance if you need to copy something like a large array inside a tight loop.
...
Assignment by Reference
...
Assignment by reference means that both variables end up pointing at the same data, and nothing is copied anywhere.
...
in my opinion everything is very clear. in the first case, a copy is created, in the second, a reference is taken and the variable refers to the same object.