PHP Attributes: Writing Custom Attribute Classes

Custom attribute classes declare legal targets and constructor arguments for structured metadata.

The examples below begin with the core behavior, then move to an application-oriented use.

How PHP Attributes: Writing Custom Attribute Classes Works

Custom attribute classes declare legal targets and constructor arguments for structured metadata.

Example 1: Basic Usage

This example uses a small input to make the main behavior visible.

<?php

#[Attribute(Attribute::TARGET_CLASS)] class ResourceName { public function __construct(public string $value) {} }
#[ResourceName("inventory")] class InventoryResource {}
echo (new ReflectionClass(InventoryResource::class))->getAttributes(ResourceName::class)[0]->newInstance()->value;

Output:

inventory

Custom attribute classes declare legal targets and constructor arguments for structured metadata.

Example 2: A Different Input

A different set of values shows the same operation in another situation.

<?php

#[Attribute(Attribute::TARGET_PARAMETER)] class TrimInput {}
class ProfileUpdater { public function rename(#[TrimInput] string $name): void {} }
$parameter = (new ReflectionMethod(ProfileUpdater::class, "rename"))->getParameters()[0];
var_dump($parameter->getAttributes(TrimInput::class) !== []);

Output:

bool(true)

Limit attribute targets with Attribute::TARGET_* and validate its constructor inputs.

Practical Example: Applying the Feature

This example shows an application-style use of the feature, with its surrounding setup visible.

<?php

#[Attribute(Attribute::TARGET_PROPERTY)] class MaxLength { public function __construct(public int $characters) {} }
class CustomerProfile { #[MaxLength(40)] public string $name = "Alex"; }
$property = new ReflectionProperty(CustomerProfile::class, "name");
echo $property->getAttributes(MaxLength::class)[0]->newInstance()->characters;

Output:

40

The code is shown for learning. Adjust the class names, inputs and error handling to suit your application.

Important Behavior and Edge Cases

• Limit attribute targets with Attribute::TARGET_* and validate its constructor inputs.
• Custom attribute classes declare legal targets and constructor arguments for structured metadata.
• Observe differences in empty inputs, invalid states and optional extension availability where relevant.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• Custom attribute classes declare legal targets and constructor arguments for structured metadata.
• Limit attribute targets with Attribute::TARGET_* and validate its constructor inputs.
• Use the example that matches the values, runtime version and dependencies in your application.

PHP Attributes: Writing Custom Attribute Classes is useful when its behavior matches the data structure and lifecycle of your PHP application. Choose it with a clear understanding of its preconditions and returned values.