`array_unshift` should allow empty reference

[mvorisek]

Description

The following code:

<?php

$arr = ['y' => []];
array_unshift($arr['x'], 'a', 'b');
print_r($arr);

https://3v4l.org/llgI6

Resulted in this output:

 Uncaught TypeError: array_unshift(): Argument #1 ($array) must be of type array, null given

But I expected this output instead:

Array
(
    [x] => Array
        (
            [0] => a
            [1] => b
        )
)

I would expect php to accept reference to null for array_unshift (and friend functions) and create empty array like $arr['x'][] = 'a' syntax does.

[Girgias]

I don't think I agree here.

The thing with those functions is that the reference parameter is an "in-out" parameter, therefore from a purely type theoretical point of view the type of the input should be the same at function entry and function exit.

This is in contrast with the reference parameter of a function like preg_match() which is an "out" parameter and uses it to provide additional info due to the return value limitation, and in those case the variable shouldn't even hold any data as it will get erased.

[mvorisek]

I fully understand your PoV and how it works. I opened this to match consistency with $arr['x'][] = 'a';. Actually, I would prefer a warning from the later much more to prevent typos.

[stramunin]

@mvorisek

to prevent typos

It's already working.
For example:
https://phpstan.org/r/8a4aea0e-a0cd-4db1-97cd-aecb02306e40

[mvorisek]

@metaliciouz I know, but not always, especially when the input comes from function parameter which usually does not have array shape defined not mentioning there are many projects not using static analysis

[stramunin]

@mvorisek

I agree. By the way, nothing prevents PHP from doing this now.
Will it work as you wanted?

function unshift(?array &$a, ...$v): void
{
    $v and $a = $v;
}

$a = ['y' => []];
unshift($a['x'], 'a', 'b');
unshift($a['z']);
unshift($a);
assert($a === ['y' => [], 'x' => ['a', 'b'], 'z' => null]);

[mvorisek]

@metaliciouz I posted this issue to handle this by the language natively, thank you for understanding it

[stramunin]

@mvorisek
Maybe you should publish a proposal (or a poll) and implement it, covering it with tests? :)