Cannot use unpacking in attribute argument list

Description

Attribute arguments are compiled into constant expressions, and evaluated only when the attribute is read through Reflection. The spread/unpacking operator ... needs a runtime array to unpack, which conflicts with this compile time, constant-only nature of attribute arguments.

Unpacking is therefore not allowed in the argument list of an attribute, even when the array being spread only contains constant values.

Example

<?php

#[Attribute]
class MyAttribute
{
    public function __construct(int $a, int $b) {}
}

$args = [1, 2];

#[MyAttribute(...$args)]
class X {}

?>

Alternatives

• List each argument explicitly, instead of unpacking an array.
• Use named arguments instead, if this improves readability.

Changed Behavior

This error may appear following an evolution in behavior, in previous versions. See