PHP: Aperçu des attributs

Aperçu des attributs

(PHP 8)

Les attributs PHP fournissent des métadonnées structurées et lisibles par machine pour les classes, méthodes, fonctions, paramètres, propriétés et constantes. Ils peuvent être inspectés à l'exécution via l'API de réflexion, permettant un comportement dynamique sans modifier le code. Les attributs offrent un moyen déclaratif d'annoter le code avec des métadonnées.

Les attributs permettent de découpler l'implémentation d'une fonctionnalité de son utilisation. Alors que les interfaces définissent une structure en imposant des méthodes, les attributs fournissent des métadonnées sur plusieurs éléments, y compris les méthodes, fonctions, propriétés et constantes. Contrairement aux interfaces, qui imposent l'implémentation de méthodes, les attributs annotent le code sans en modifier la structure.

Les attributs peuvent compléter ou remplacer des méthodes d'interface optionnelles en fournissant des métadonnées plutôt qu'une structure imposée. Prenons une interface ActionHandler qui représente une opération dans une application. Certaines implémentations peuvent nécessiter une étape d'initialisation, tandis que d'autres non. Plutôt que d'obliger toutes les classes implémentant ActionHandler à définir une méthode setUp(), un attribut peut indiquer les besoins en initialisation. Cette approche augmente la flexibilité en permettant d'appliquer les attributs plusieurs fois si nécessaire.

Exemple #1 Implémentation de méthodes optionnelles d'une interface avec des attributs

<?php
interface ActionHandler
{
    public function execute();
}

#[Attribute]
class SetUp {}

class CopyFile implements ActionHandler
{
    public string $fileName;
    public string $targetDirectory;

    #[SetUp]
    public function fileExists()
    {
        if (!file_exists($this->fileName)) {
            throw new RuntimeException("Le fichier n'existe pas.");
        }
    }

    #[SetUp]
    public function targetDirectoryExists()
    {
        if (!file_exists($this->targetDirectory)) {
            mkdir($this->targetDirectory);
        } elseif (!is_dir($this->targetDirectory)) {
            throw new RuntimeException("Le répertoire cible $this->targetDirectory n'est pas un répertoire.");
        }
    }

    public function execute()
    {
        copy($this->fileName, $this->targetDirectory . '/' . basename($this->fileName));
    }
}

function executeAction(ActionHandler $actionHandler)
{
    $reflection = new ReflectionObject($actionHandler);

    foreach ($reflection->getMethods() as $method) {
        $attributes = $method->getAttributes(SetUp::class);

        if (count($attributes) > 0) {
            $methodName = $method->getName();

            $actionHandler->$methodName();
        }
    }

    $actionHandler->execute();
}

$copyAction = new CopyFile();
$copyAction->fileName = "/tmp/foo.jpg";
$copyAction->targetDirectory = "/home/user";

executeAction($copyAction);

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User Contributed Notes 2 notes

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Harshdeep ¶

3 years ago

While the example displays us what we can accomplish with attributes, it should be kept in mind that the main idea behind attributes is to attach static metadata to code (methods, properties, etc.). This metadata often includes concepts such as "markers" and "configuration". For example, you can write a serializer using reflection that only serializes marked properties (with optional configuration, such as field name in serialized file). This is reminiscent of serializers written for C# applications.That said, full reflection and attributes go hand in hand. If your use case is satisfied by inheritance or interfaces, prefer that. The most common use case for attributes is when you have no prior information about the provided object/class.<?phpinterface JsonSerializable{    public function toJson() : array;}?>versus, using attributes,<?php#[Attribute]class JsonSerialize {    public function __constructor(public ?string $fieldName = null) {}}class VersionedObject{   #[JsonSerialize]    public const version = '0.0.1';}public class UserLandClass extends VersionedObject{    #[JsonSerialize('call it Jackson')]    public string $myValue;}?>The example above is a little extra convoluted with the existence of the VersionedObject class as I wished to display that with attribute mark ups, you do not need to care how the base class manages its attributes (no call to parent in overriden method).

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Florian Krmer ¶

2 years ago

I've tried Harshdeeps example and it didn't run out of the box and I think it is not complete, so I wrote a complete and working naive example regarding attribute based serialization.<?phpdeclare(strict_types=1);#[Attribute(Attribute::TARGET_CLASS_CONSTANT|Attribute::TARGET_PROPERTY)]class JsonSerialize{    public function __construct(public ?string $fieldName = null) {}}class VersionedObject{    #[JsonSerialize]    public const version = '0.0.1';}class UserLandClass extends VersionedObject{    protected string $notSerialized = 'nope';    #[JsonSerialize('foobar')]    public string $myValue = '';    #[JsonSerialize('companyName')]    public string $company = '';    #[JsonSerialize('userLandClass')]    protected ?UserLandClass $test;    public function __construct(?UserLandClass $userLandClass = null)    {        $this->test = $userLandClass;    }}class AttributeBasedJsonSerializer {    protected const ATTRIBUTE_NAME = 'JsonSerialize';    public function serialize($object)    {        $data = $this->extract($object);        return json_encode($data, JSON_THROW_ON_ERROR);    }    protected function reflectProperties(array $data, ReflectionClass $reflectionClass, object $object)    {        $reflectionProperties = $reflectionClass->getProperties();        foreach ($reflectionProperties as $reflectionProperty) {            $attributes = $reflectionProperty->getAttributes(static::ATTRIBUTE_NAME);            foreach ($attributes as $attribute) {                $instance = $attribute->newInstance();                $name = $instance->fieldName ?? $reflectionProperty->getName();                $value = $reflectionProperty->getValue($object);                if (is_object($value)) {                    $value = $this->extract($value);                }                $data[$name] = $value;            }        }        return $data;    }    protected function reflectConstants(array $data, ReflectionClass $reflectionClass)    {        $reflectionConstants = $reflectionClass->getReflectionConstants();        foreach ($reflectionConstants as $reflectionConstant) {            $attributes = $reflectionConstant->getAttributes(static::ATTRIBUTE_NAME);            foreach ($attributes as $attribute) {                $instance = $attribute->newInstance();                $name = $instance->fieldName ?? $reflectionConstant->getName();                $value = $reflectionConstant->getValue();                if (is_object($value)) {                    $value = $this->extract($value);                }                $data[$name] = $value;            }        }        return $data;    }    protected function extract(object $object)    {        $data = [];        $reflectionClass = new ReflectionClass($object);        $data = $this->reflectProperties($data, $reflectionClass, $object);        $data = $this->reflectConstants($data, $reflectionClass);        return $data;    }}$userLandClass = new UserLandClass();$userLandClass->company = 'some company name';$userLandClass->myValue = 'my value';$userLandClass2 = new UserLandClass($userLandClass);$userLandClass2->company = 'second';$userLandClass2->myValue = 'my second value';$serializer = new AttributeBasedJsonSerializer();$json = $serializer->serialize($userLandClass2);var_dump(json_decode($json, true));

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