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?

I would be thankful if the downvoters would point out the problems with my question. — totymedli, Apr 11 '18 at 19:31
Possible duplicate of [Reference - What does this error mean in PHP?](https://stackoverflow.com/questions/12769982/reference-what-does-this-error-mean-in-php) — emix, Mar 31 '19 at 16:55
@emix How on Earth is this a duplicate of that? That thread doesn't contain anything even slightly related to argument unpacking. — totymedli, Mar 31 '19 at 21:21

totymedli · Accepted Answer · 2019-03-31T16:42:13.720

12

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

edited Mar 31 '19 at 16:42

answered Apr 11 '18 at 18:06

totymedli

26,417
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5

You can however unpack after unpacking, so `var_dump(...$params, ...[$extraVariable])` works too. – user3942918 Apr 11 '18 at 18:14
@PaulCrovella Indeed, that is a more concise solution! Thanks. – totymedli Apr 11 '18 at 19:41

score 3 · Answer 2 · answered Apr 11 '18 at 18:17

3

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);

answered Apr 11 '18 at 18:17

AbraCadaver

77,023
7
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See the bolded words? "that calls another function with the same arguments **and a new one at the end**" – user3942918 Apr 11 '18 at 18:19
1

Hi, good point, but if for him the order is important, he wants `$extraVariable` to be in the end? – ankabot Apr 11 '18 at 18:19
@PaulCrovella: Seems like an unreasonable constraint, but they have the other answer. – AbraCadaver Apr 11 '18 at 18:52
This is a nice workaround, but my question explicitly stated "and a new one **at the end**". – totymedli Apr 11 '18 at 19:33

score 1 · Answer 3 · answered Mar 31 '19 at 15:48

1

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]);

answered Mar 31 '19 at 15:48

Edward Surov

339
1
2

PHP Fatal error: Cannot use positional argument after argument unpacking

Task

What have I tried

Problem

3 Answers3

tl;dr

Explanation

Linked

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