How to declare output parameter in callable type?

[rzvc]

I'm trying to declare a callable for the following function:

function test(string &$a) : void
{
    $a = 'asdf';
}

I've read the discussion from 2018 regarding the callable syntax and the output via parameter reference was mentioned but I think it was overlooked in the initial implementation. Any ideas if it's possible to declare it now?

[AndrolGenhald]

Like this? Here's the documentation.

Edit: Or do you mean you want to annotate a callable that has its own @param-out? Hmm, not sure if that is possible yet...

[rzvc]

No, what I want to declare is something like this:

/** @var callable(&string) $callable */
$callable($a);    // Now $a is 'string'.

Sorry for not being clear enough the first time.

[AndrolGenhald]

So basically like an annotation to describe a function like:

/** @param-out string $bar */
function foo(mixed &$bar): void
{
    ...
}

ie callable(&in<mixed>+out<string>) would accept "foo" as a valid type in that case? (just to throw around a random syntax, not actually suggesting that)

It was clear enough if I've understood it now, it just took me a minute to catch on.

[rzvc]

Yep, that's it.

The specification was discussed in #580.