Re: Callable arguments cannot have default value
| From: | Robert Landers | Date: | Tue, 28 Nov 2023 09:45:43 +0000 |
| Subject: | Re: Callable arguments cannot have default value | ||
| References: | 1 | Groups: | php.internals |
| Request: | Send a blank email to internals+get-121819@lists.php.net to get a copy of this message | ||
On Tue, Nov 28, 2023 at 12:59 AM Sergii Shymko <sergey@shymko.net> wrote:
>
> Hi,
>
> Wanted to bring up an inconsistent behavior of callable arguments compared to arguments of
> other types.
> Callable argument cannot have a default value (tested string or array types - both are not
> permitted).
> The same exact value works perfectly fine when passed dynamically, it just cannot be specified
> as a default.
> The workaround is to remove the type annotation which is obviously undesirable.
>
> Here’s an example:
> declare(strict_types=1);
> function test(callable $idGenerator = 'session_create_id') {
> $id = $idGenerator();
> // ...
> }
>
> The function/method declaration above produces the following error on all PHP versions:
> Fatal error: Cannot use string as default value for parameter $idGenerator 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) {…}
> test('session_create_id’);
>
> Is there a specific architectural limitation causing this that's hard/impossible to
> overcome?
>
> I’m 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 these 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/impossible 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 $closure = new wrapper('hello')) {
($closure)();
}
test();