Recreate PHP Objects Using __set_state and var_export

This article explains how to use PHP’s __set_state() magic method to restore and recreate objects that have been exported using the var_export() function. You will learn how var_export() generates an executable string representation of an object, and how implementing the static __set_state() method allows your classes to instantiate and populate themselves from this exported data.

Understanding var_export() and __set_state()

The var_export() function gets structured information about a variable. When exporting an object, it outputs code that calls a static method named __set_state().

To recreate the object from this exported string, the target class must implement the __set_state() magic method. This method is called automatically when the exported PHP code is evaluated or included.

Requirements for __set_state()

• It must be declared as static.
• It must accept a single argument: an associative array containing the exported property names and their corresponding values.
• It must return an instance of the class.

Step-by-Step Implementation

Here is how to implement the __set_state() method and use it to recreate an exported object.

1. Define the Class with __set_state()

In your class, define the static __set_state() method. It reads the array of properties and returns a new object instance.

class User 
{
    public $username;
    public $email;

    public function __construct($username, $email) 
    {
        $this->username = $username;
        $this->email = $email;
    }

    // The magic method called by evaluated var_export code
    public static function __set_state(array $properties) 
    {
        $user = new self($properties['username'], $properties['email']);
        return $user;
    }
}

2. Export the Object

Instantiate your object and pass it to var_export(). Setting the second argument of var_export() to true returns the representation as a string instead of outputting it directly.

$originalUser = new User('johndoe', 'john@example.com');

// Export the object to a string of PHP code
$exportedCode = var_export($originalUser, true);

echo $exportedCode;

Output of $exportedCode:

User::__set_state(array(
   'username' => 'johndoe',
   'email' => 'john@example.com',
))

3. Recreate the Object

To turn the exported code back into a live PHP object, you run the generated code. In practice, this is usually done by writing the exported string to a configuration file and loading it later using include or require.

Method A: Writing to and including a file (Recommended)

// Save the exported code to a file
file_put_contents('user_cache.php', '<?php return ' . $exportedCode . ';');

// Recreate the object by including the file
$recreatedUser = include 'user_cache.php';

var_dump($recreatedUser);

Method B: Using eval() (For quick execution)

// Recreate the object directly from the string using eval()
$recreatedUser = eval("return $exportedCode;");

var_dump($recreatedUser);

Both methods return a fully constructed instance of the User class with the original properties restored.