__clone for object copying in PHP - Step-by-Step Execution

Concept Flow - __clone for object copying

Create original object

↓

Call clone keyword

↓

__clone method runs?

No→Shallow copy created

Yes↓

__clone method customizes copy

↓

New cloned object ready

When you clone an object, PHP makes a copy. If __clone exists, it runs to customize the copy.

Execution Sample

PHP

<?php
class Box {
  public $color;
  public function __clone() {
    $this->color = 'cloned ' . $this->color;
  }
}
$box1 = new Box();
$box1->color = 'red';
$box2 = clone $box1;
echo $box2->color;
?>

This code clones a Box object and changes the color property in the clone using __clone.

Execution Table

Step	Action	Object State	Output
1	Create $box1	box1.color = null
2	Set $box1->color = 'red'	box1.color = 'red'
3	Clone $box1 to $box2	box2.color = 'red' (before __clone)
4	__clone runs on $box2	box2.color = 'cloned red'
5	echo $box2->color	box2.color = 'cloned red'	cloned red
6	End	No more actions

💡 Execution stops after echoing the cloned object's modified color property.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
$box1->color	null	'red'	'red'	'red'	'red'
$box2->color	undefined	undefined	'red'	'cloned red'	'cloned red'

Key Moments - 3 Insights

Why does $box2->color change after cloning?

Because the __clone method runs on the new object and modifies the color property as shown in step 4 of the execution_table.

Does cloning change the original object $box1?

No, cloning creates a new object. $box1 remains unchanged as seen in variable_tracker where $box1->color stays 'red'.

What happens if __clone method is not defined?

PHP makes a shallow copy without changes. The cloned object's properties remain the same as the original before any __clone customization.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of $box2->color immediately after cloning but before __clone runs?

A 'cloned red'

B 'red'

C null

D undefined

💡 Hint

Check step 3 in the execution_table where cloning happens before __clone modifies the object.

At which step does the __clone method modify the cloned object?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the execution_table row describing __clone running on $box2.

If __clone was removed, what would be the output at step 5?

A 'red'

B 'cloned red'

C null

D Error

💡 Hint

Without __clone, the cloned object keeps the original property values as shown in the explanation of key moments.

Concept Snapshot

__clone keyword creates a copy of an object.
If __clone() method exists, it runs on the new copy.
Use __clone to customize cloned object properties.
Original object stays unchanged.
Syntax: $copy = clone $original;
__clone is called automatically during cloning.

Full Transcript

In PHP, cloning an object creates a new object with the same properties. When you use the clone keyword, PHP copies the original object. If the class has a __clone method, PHP runs it on the new object to let you change properties or do other setup. This does not affect the original object. For example, if you have a Box object with a color property set to 'red', cloning it creates a new Box with color 'red'. Then __clone can change the color to 'cloned red'. The original Box remains 'red'. This helps when you want a similar object but with some differences. The execution table shows each step: creating the original, setting color, cloning, running __clone, and printing the cloned color. The variable tracker shows how $box1 and $box2 colors change. Key moments clarify why the clone changes only the new object and what happens without __clone. The quiz tests understanding of when and how __clone runs and what values change.