Attribute syntax

    There are several parts to the attributes syntax. First, an attribute declaration is always enclosed with a starting #[ and a corresponding ending ]. Inside, one or many attributes are listed, separated by comma. The attribute name is an unqualified, qualified or fully-qualified name as described in Using Namespaces Basics. Arguments to the attribute are optional, but are enclosed in the usual parenthesis (). Arguments to attributes can only be literal values or constant expressions. Both positional and named arguments syntax can be used.

    Attribute names and their arguments are resolved to a class and the arguments are passed to its constructor, when an instance of the attribute is requested through the Reflection API. As such a class should be introduced for each attribute.

    Example #1 Attribute Syntax

    <?php
    // a.php
    namespace MyExample;

    use     Attribute;

    #[    Attribute]
    class     MyAttribute
    {
    const     VALUE = 'value';

    private     $value;

    public function     __construct($value = null)
    {
    $this->value = $value;
    }
    }

    // b.php

    namespace Another;

    use     MyExample\MyAttribute;

    #[    MyAttribute]
    #[    \MyExample\MyAttribute]
    #[    MyAttribute(1234)]
    #[    MyAttribute(value: 1234)]
    #[    MyAttribute(MyAttribute::VALUE)]
    #[    MyAttribute(array("key" => "value"))]
    #[    MyAttribute(100 + 200)]
    class     Thing
    {
    }

    #[    MyAttribute(1234), MyAttribute(5678)]
    class     AnotherThing
    {
    }

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    User Contributed Notes 1 note

    up
    3
    yarns dot purport0n at icloud dot com
    8 months ago
    It wasn't obvious to me for a while but you can subclass attributes

    https://3v4l.org/TrMTe

    <?php

    #[Attribute(Attribute::TARGET_PROPERTY)]
    class     PropertyAttributes
    {
    public function     __construct(
    public readonly ?    string $name = null,
    public readonly ?    string $label = null,
    ) {}
    }

    #[    Attribute(Attribute::TARGET_PROPERTY)]
    class     IntegerPropertyAttributes extends PropertyAttributes
    {
    public function     __construct(
    ?    string $name = null,
    ?    string $label = null,
    public readonly ?    int $default = null,
    public readonly ?    int $min = null,
    public readonly ?    int $max = null,
    public readonly ?    int $step = null,
    ) {
    parent::__construct($name, $label);
    }
    }

    #[    Attribute(Attribute::TARGET_PROPERTY)]
    class     FloatPropertyAttributes extends PropertyAttributes
    {
    public function     __construct(
    ?    string $name = null,
    ?    string $label = null,
    public readonly ?    float $default = null,
    public readonly ?    float $min = null,
    public readonly ?    float $max = null,
    ) {
    parent::__construct($name, $label);
    }
    }

    class     MyClass
    {
    #[    IntegerPropertyAttributes('prop', 'property: ', 5, 0, 10, 1)]
    public     int $prop;
    }

    $refl = new ReflectionProperty('MyClass', 'prop');
    $attributes = $refl->getAttributes();

    foreach (    $attributes as $attribute) {
    var_dump($attribute->getName());
    var_dump($attribute->getArguments());
    var_dump($attribute->newInstance());
    }
    ?>
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