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References: <AA17AB82-695F-4E4B-ABDA-B8AA085466AC@shymko.net>
In-Reply-To: <AA17AB82-695F-4E4B-ABDA-B8AA085466AC@shymko.net>
Date: Tue, 28 Nov 2023 10:45:43 +0100
Message-ID: <CAPzBOBP6rCfi3GwGYXXOzgjYNWfJg2YcnrCEUxzaR0gLu2qjAA@mail.gmail.com>
To: Sergii Shymko <sergey@shymko.net>
Cc: internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Callable arguments cannot have default value
From: landers.robert@gmail.com (Robert Landers)

On Tue, Nov 28, 2023 at 12:59=E2=80=AFAM Sergii Shymko <sergey@shymko.net> =
wrote:
>
> Hi,
>
> Wanted to bring up an inconsistent behavior of callable arguments compare=
d to arguments of other types.
> Callable argument cannot have a default value (tested string or array typ=
es - both are not permitted).
> The same exact value works perfectly fine when passed dynamically, it jus=
t cannot be specified as a default.
> The workaround is to remove the type annotation which is obviously undesi=
rable.
>
> Here=E2=80=99s an example:
> declare(strict_types=3D1);
> function test(callable $idGenerator =3D 'session_create_id') {
>     $id =3D $idGenerator();
>     // ...
> }
>
> The function/method declaration above produces the following error on all=
 PHP versions:
> Fatal error: Cannot use string as default value for parameter $idGenerato=
r of type callable in /tmp/preview on line 4
>
> Note that the exact same string argument can be passed without any issue:
> function test(callable $idGenerator) {=E2=80=A6}
> test('session_create_id=E2=80=99);
>
> Is there a specific architectural limitation causing this that's hard/imp=
ossible to overcome?
>
> I=E2=80=99m aware that class properties cannot be annotated with callable=
 - another unfortunate limitation.
> Callable is not a real type like other primitive types which causes all t=
hese inconsistencies, correct?
> Callable properties (separate topic) may be a challenge, but can at least=
 argument defaults be supported?
>
> Regards,
> Sergii Shymko

I stopped using "callable" a long time ago. These days I use \Closure
and it works in all the same places (including properties).

If you want to accept a callable string, you need to change the type
to \Closure|string and verify it with `is_callable()`.

> Is there a specific architectural limitation causing this that's hard/imp=
ossible to overcome?

IIRC, default arguments must be compile-time constant, and this isn't,
apparently:

session_create_id(...)

You can also do something like this:

function hello() {
    echo "hi\n";
}

class wrapper {
    public function __construct(public \Closure|string $closure) {
        is_callable($closure) ?: throw new
InvalidArgumentException('closure must be callable');
    }
    public function __invoke() {
        return ($this->closure)();
    }
}

function test(wrapper|Closure $closure =3D new wrapper('hello')) {
    ($closure)();
}

test();