Using PHP attributes easily

PHP attributes are a new feature included in the last php 8 version which allow us to easily add metadata to our classes, methods and properties.

Creating an attribute is easy, we only have to create a class, define its properties and mark it as attribute. Let's see an example

    #[\Attribute]
    class IsBackground
    {
        public function __construct(
            public readonly ?int $delay = null
        ){ }
     }

In the above code, we've created an attribute called IsBackground which holds one parameter: delay.

Now let's see how we could use it. Imagine we have a class called Operation which we want to decorate as "IsBackground".

    #[IsBackground]
    class Operation {

        // properties and methods
    }

As we can see, it's already marked simply using #[IsBackground] at the top of the class.

Now, let's see how to read attribute data:

     $reflectionClass = new \ReflectionClass(new Operation());
     $attributes = $reflectionClass->getAttributes(IsBackground::class);
     $attr = reset($attributes);
     $attrObject = $attr->newInstance();

     echo $attrObject->delay;

When we decorated Operation with IsBackground attribute we defined no delay. In order to set a delay, we would change Operation class like this:

#[IsBackground(delay: 600)]
class Operation {

    // properties and methods
}

If you want to learn how i used PHP attributes to define API operations, you can read this post or read my book: Building an operation-oriented api using PHP and the Symfony framework

Comments

[Yannick Chenot]

Thanks for the simple example. Now, what would be the advantage of doing this over, say, a Background interface with a public getDelay() method, for instance?

[Nacho Colomina Torregrosa]

Hi Yannick, Thanks to you too.

You can use attributes when you want to add metadata to a class but it is not necessary the class to follow a contract. If the class has to follow a contract then you would have to use an interface. Let's think about symfony messenger handlers. At the first versions handlers needed to implement MessageHandlerInterface but that interface did not hold any method. Now, to define a message handler you use_ #[AsMessageHandler] _attribute

[Christine Belzie]

Hi @icolomina. Welcome to Dev! It’s nice to meet you. I’m not familiar with phps but the way you explained the first code snippet made it a bit easier to understand. Keep it up! :)

[Nacho Colomina Torregrosa]

Many thanks Christine! It's nice to write here :)

[Hoshimxon]

I think last line should be echo $attrObject->delay; not echo $attr->delay;

[Nacho Colomina Torregrosa]

Yes, you are right. Thanks !!