The VarExporter Component

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The VarExporter Component

The VarExporter component exports any serializable PHP data structure to plain PHP code and allows to instantiate and populate objects without calling their constructors.

Installation

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$ composer require --dev symfony/var-exporter

Note

If you install this component outside of a Symfony application, you must require the vendor/autoload.php file in your code to enable the class autoloading mechanism provided by Composer. Read this article for more details.

Exporting/Serializing Variables

The main feature of this component is to serialize PHP data structures to plain PHP code, similar to PHP's var_export function:

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use Symfony\Component\VarExporter\VarExporter;

$exported = VarExporter::export($someVariable);
// store the $exported data in some file or cache system for later reuse
$data = file_put_contents('exported.php', '<?php return '.$exported.';');

// later, regenerate the original variable when you need it
$regeneratedVariable = require 'exported.php';

The reason to use this component instead of serialize() or igbinary is performance: thanks to OPcache, the resulting code is significantly faster and more memory efficient than using unserialize() or igbinary_unserialize().

In addition, there are some minor differences:

  • If the original variable defines them, all the semantics associated with serialize() (such as __wakeup(), __sleep(), and Serializable) are preserved (var_export() ignores them);
  • References involving SplObjectStorage, ArrayObject or ArrayIterator instances are preserved;
  • Missing classes throw a ClassNotFoundException instead of being unserialized to PHP_Incomplete_Class objects;
  • Reflection*, IteratorIterator and RecursiveIteratorIterator classes throw an exception when being serialized.

The exported data is a PSR-2 compatible PHP file. Consider for example the following class hierarchy:

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abstract class AbstractClass
{
    protected $foo;
    private $bar;

    protected function setBar($bar)
    {
        $this->bar = $bar;
    }
}

class ConcreteClass extends AbstractClass
{
    public function __construct()
    {
        $this->foo = 123;
        $this->setBar(234);
    }
}

When exporting the ConcreteClass data with VarExporter, the generated PHP file looks like this:

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<?php
return \Symfony\Component\VarExporter\Internal\Hydrator::hydrate(
    $o = [
        clone (\Symfony\Component\VarExporter\Internal\Registry::$prototypes['Symfony\\Component\\VarExporter\\Tests\\ConcreteClass'] ?? \Symfony\Component\VarExporter\Internal\Registry::p('Symfony\\Component\\VarExporter\\Tests\\ConcreteClass')),
    ],
    null,
    [
        'Symfony\\Component\\VarExporter\\Tests\\AbstractClass' => [
            'foo' => [
                123,
            ],
            'bar' => [
                234,
            ],
        ],
    ],
    $o[0],
    []
);

Instantiating PHP Classes

The other main feature provided by this component is an instantiator which can create objects and set their properties without calling their constructors or any other methods:

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use Symfony\Component\VarExporter\Instantiator;

// creates an empty instance of Foo
$fooObject = Instantiator::instantiate(Foo::class);

// creates a Foo instance and sets one of its properties
$fooObject = Instantiator::instantiate(Foo::class, ['propertyName' => $propertyValue]);

// creates a Foo instance and sets a private property defined on its parent Bar class
$fooObject = Instantiator::instantiate(Foo::class, [], [
    Bar::class => ['privateBarProperty' => $propertyValue],
]);

Instances of ArrayObject, ArrayIterator and SplObjectHash can be created by using the special "\0" property name to define their internal value:

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// Creates an SplObjectHash where $info1 is associated with $object1, etc.
$theObject = Instantiator::instantiate(SplObjectStorage::class, [
    "\0" => [$object1, $info1, $object2, $info2...],
]);

// creates an ArrayObject populated with $inputArray
$theObject = Instantiator::instantiate(ArrayObject::class, [
    "\0" => [$inputArray],
]);
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.