It is recommended to define a separate class for each attribute. In the simplest
case, an empty class with the #[Attribute] declaration is sufficient.
The attribute can be imported from the global namespace using a use
statement.
Example #1 Simple Attribute Class
<?php
namespace Example;
use Attribute;
#[Attribute]
class MyAttribute
{
}
To restrict the types of declarations an attribute can be applied to,
pass a bitmask as the first argument to the #[Attribute]
declaration.
Example #2 Using target specification to restrict where attributes can be used
<?php
namespace Example;
use Attribute;
#[Attribute(Attribute::TARGET_METHOD | Attribute::TARGET_FUNCTION)]
class MyAttribute
{
}Declaring MyAttribute on another type will now throw an exception during the call to ReflectionAttribute::newInstance()
The following targets can be specified:
Attribute::TARGET_CLASS Attribute::TARGET_FUNCTION Attribute::TARGET_METHOD Attribute::TARGET_PROPERTY Attribute::TARGET_CLASS_CONSTANT Attribute::TARGET_PARAMETER Attribute::TARGET_ALL
By default, an attribute can only be used once per declaration. To allow
an attribute to be repeatable, specify it in the bitmask of the
#[Attribute] declaration using the
Attribute::IS_REPEATABLE flag.
Example #3 Using IS_REPEATABLE to allow attribute on a declaration multiple times
<?php
namespace Example;
use Attribute;
#[Attribute(Attribute::TARGET_METHOD | Attribute::TARGET_FUNCTION | Attribute::IS_REPEATABLE)]
class MyAttribute
{
}#! Require PHP >= 8.0
#! This is a Sample
<?php
declare(strict_types = 1);
#[Attribute]
class Foo
{
function __construct(){
echo "Running " . __METHOD__ . PHP_EOL;
}
}
#[Attribute(Attribute::TARGET_CLASS|Attribute::IS_REPEATABLE)]
class Bar {
function __construct(?string ...$args){
echo "Running " . __METHOD__ ,
" args: " . implode(", ", $args) . PHP_EOL;
}
}
#[Attribute(Attribute::TARGET_ALL)]
class Baz {
function __construct(
private string $parameter
){
echo "Running " . __METHOD__ ,
" arg: " . $this->parameter . PHP_EOL;
}
}
#[Foo] // [0]
#[Bar] // [1]
#[Bar("Banana")] // [2]
#[Bar("Banana", "Apple", "Lemon", "Grape")] // [3]
#[Baz("The Only One")] // [4]
class Qux
{
}
// Getting class attribute with ReflectionClass
$ref = new ReflectionClass(Qux::class);
$attrs = $ref->getAttributes(); // Array of attributes
$attrs[0]->newInstance(); // "Running Foo::__construct"
$attrs[1]->newInstance(); // "Running Bar::__construct args: "
$attrs[2]->newInstance(); // "Running Bar::__construct args: Banana"
$attrs[3]->newInstance(); // "Running Bar::__construct args: Banana, Apple, Lemon, Grape"
$attrs[4]->newInstance(); // "Running Baz::__construct arg: The Only One"