No Unknown For array_merge()

<?php

function foo($x, ...$array) {
    print_r($x);
    print_r($array);
}

$a = ['w' => 'w', 'x' => 'x'];

foo(...$a);

print_r(array_merge(...$a));
// array_merge() does not accept unknown named parameters

A PHP variadic argument collects all the unused named parameters, along with their key. That way, it is possible to handle them with their name inside the method.

On the other hand, array_merge(), and some cousins, refuse them, and emits a Fatal error. There, it is important to use array_values() to avoid named parameters.

See Also

• array_merge (PHP manual)
• Functions arguments
• array_merge() doesn’t accept unknown named parameters [Try me]

PHP Error Messages

• array_merge() does not accept unknown named parameters

PHP Features

• ellipsis
• named-parameter

Last updated: 11 October 2026