array_merge() does not accept unknown named parameters

Description

array_merge() accepts one parameter, called \$arrays. In fact, it is a variadic parameter, so this parameter may be repeated as needed. Yet, there is only one name for it.

When using array_merge() with a variadic argument, PHP tries to match the keys of the array with the parameters, and in this case, fails for all but one: $arrays.

The solution is to spread the array, after removing the string keys: with integer keys, PHP will not check the names.

There are several PHP native functions that behave like that: array_merge(), array_diff_key(), etc. In fact, any native method which has a variadic parameter.

PHP doesn’t emit an error when spreading an array with unkown keys in a custom function.

Example

<?php

$a = ['x' => [1], 'y' => [3]];

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

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

?>

Solutions

• Apply array_values() to the array that is used with array_merge().