99 lines
3.9 KiB
Markdown
99 lines
3.9 KiB
Markdown
VarExporter Component
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=====================
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The VarExporter component provides various tools to deal with the internal state
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of objects:
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- `VarExporter::export()` allows exporting any serializable PHP data structure to
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plain PHP code. While doing so, it preserves all the semantics associated with
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the serialization mechanism of PHP (`__wakeup`, `__sleep`, `Serializable`,
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`__serialize`, `__unserialize`);
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- `Instantiator::instantiate()` creates an object and sets its properties without
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calling its constructor nor any other methods;
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- `Hydrator::hydrate()` can set the properties of an existing object;
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- `Lazy*Trait` can make a class behave as a lazy-loading ghost or virtual proxy.
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VarExporter::export()
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---------------------
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The reason to use `VarExporter::export()` *vs* `serialize()` or
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[igbinary](https://github.com/igbinary/igbinary) is performance: thanks to
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OPcache, the resulting code is significantly faster and more memory efficient
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than using `unserialize()` or `igbinary_unserialize()`.
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Unlike `var_export()`, this works on any serializable PHP value.
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It also provides a few improvements over `var_export()`/`serialize()`:
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* the output is PSR-2 compatible;
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* the output can be re-indented without messing up with `\r` or `\n` in the data;
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* missing classes throw a `ClassNotFoundException` instead of being unserialized
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to `PHP_Incomplete_Class` objects;
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* references involving `SplObjectStorage`, `ArrayObject` or `ArrayIterator`
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instances are preserved;
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* `Reflection*`, `IteratorIterator` and `RecursiveIteratorIterator` classes
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throw an exception when being serialized (their unserialized version is broken
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anyway, see https://bugs.php.net/76737).
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Instantiator and Hydrator
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-------------------------
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`Instantiator::instantiate($class)` creates an object of the given class without
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calling its constructor nor any other methods.
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`Hydrator::hydrate()` sets the properties of an existing object, including
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private and protected ones. For example:
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```php
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// Sets the public or protected $object->propertyName property
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Hydrator::hydrate($object, ['propertyName' => $propertyValue]);
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// Sets a private property defined on its parent Bar class:
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Hydrator::hydrate($object, ["\0Bar\0privateBarProperty" => $propertyValue]);
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// Alternative way to set the private $object->privateBarProperty property
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Hydrator::hydrate($object, [], [
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Bar::class => ['privateBarProperty' => $propertyValue],
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]);
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```
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Lazy Proxies
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------------
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Since version 8.4, PHP provides support for lazy objects via the reflection API.
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This native API works with concrete classes. It doesn't with abstracts nor with
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internal ones.
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This components provides helpers to generate lazy objects using the decorator
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pattern, which works with abstract or internal classes and with interfaces:
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```php
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$proxyCode = ProxyHelper::generateLazyProxy(new ReflectionClass(AbstractFoo::class));
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// $proxyCode should be dumped into a file in production envs
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eval('class FooLazyProxy'.$proxyCode);
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$foo = FooLazyProxy::createLazyProxy(initializer: function (): AbstractFoo {
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// [...] Use whatever heavy logic you need here
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// to compute the $dependencies of the $instance
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$instance = new Foo(...$dependencies);
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// [...] Call setters, etc. if needed
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return $instance;
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});
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// $foo is now a lazy-loading decorator object. The initializer will
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// be called only when and if a *method* is called.
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```
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In addition, this component provides traits and methods to aid in implementing
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the ghost and proxy strategies in previous versions of PHP. Those are deprecated
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when using PHP 8.4.
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Resources
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---------
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* [Documentation](https://symfony.com/doc/current/components/var_exporter.html)
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* [Contributing](https://symfony.com/doc/current/contributing/index.html)
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* [Report issues](https://github.com/symfony/symfony/issues) and
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[send Pull Requests](https://github.com/symfony/symfony/pulls)
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in the [main Symfony repository](https://github.com/symfony/symfony)
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