PHP Fatal error: Cannot use positional argument after argument unpacking

Question

Task

I would like to write a function with variable number of parameters (using ...) that calls another function with the same arguments and a new one at the end. Order is important! The example below is just for demonstration.

What have I tried

function foo(...$params) {
    $extraVariable = 6;
    var_dump(...$params, $extraVariable);
}
foo(2, 4, 1, 4);

Problem

When I run it, I get the following error message:

PHP Fatal error: Cannot use positional argument after argument unpacking in /home/user/main.php on line 3

How can I achieve my goal?

Answer 1

tl;dr

Unpacking after arguments is not allowed by design, but there are 2 workarounds:

• Create an array from the new element and unpack that as Paul suggested:

  function foo(...$params) {
      $extraVariable = 6;
      var_dump(...$params, ...[$extraVariable]);
  }
  

• Push the new element to the params:

  function foo(...$params) {
      $extraVariable = 6;
      $params[] = $extraVariable;
      var_dump(...$args);
  }
  

Explanation

PHP simply doesn't support this. You can see the unit test that checks this behavior:

--TEST--
Positional arguments cannot be used after argument unpacking
--FILE--
<?php

var_dump(...[1, 2, 3], 4);

?>
--EXPECTF--
Fatal error: Cannot use positional argument after argument unpacking in %s on line %d

Answer 2

See the bolded word?

PHP Fatal error: Cannot use positional argument after argument unpacking in /home/user/main.php on line 3

So use it before unpacking.

var_dump($extraVariable, ...$params);

Answer 3

There is a workaround. You cannot use positional arguments after unpacked one, but you can use several unpacked arguments; so you can just wrap your variable(s) in array literal and unwrap it like this:

var_dump(...$params, ...[$extraVariable]);