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Date: Sat, 13 Mar 2021 10:21:27 +0000
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To: internals@lists.php.net
Message-ID: <9C9FB480-6BAB-4318-8AC2-17A511A28866@gmail.com>
Subject: Re: [PHP-DEV] Add support for ::class to constant()
From: rowan.collins@gmail.com (Rowan Tommins)

On 9 March 2021 22:15:49 GMT, "K=C3=A9vin Dunglas" <kevin@dunglas=2Efr> wro=
te:
>Hi folks,
>
>Currently, it's not possible to use the ::class special constant with
>the
>constant() function=2E This doesn't work:
>
>var_dump(
>  constant('\DateTime::class')
>);


While this looks logical at first glance, I'm not sure this can actually w=
ork, because you are asking at runtime for information which only exists at=
 compile time=2E This is similar to other "magic" constants such as __LINE_=
_=2E

The only cases where ::class is calculated at runtime are self::class, and=
 the recently added $obj::class, where $obj is an object instance=2E All ot=
her uses are expanded by the compiler based on the namespace and use statem=
ents in effect at that point in the code=2E If you try to calculate it at r=
untime, it would end up being evaluated where the call to constant() happen=
s, which wouldn't actually have those namespace and use directives in effec=
t=2E

Consider this example:


namespace Acme\Foo {
    use Some\Other\Baz;

    function test(string $class) {
        echo constant($class =2E '::class');
    }
}
namespace Acme\Different {
    use Acme\Bar\Baz as BarBaz;
   =20
    echo Baz::class, PHP_EOL;
    echo BarBaz::class, PHP_EOL;

    echo test('Baz');
    echo test('BarBaz');
}


Logically, the calls to test() should result in the same output as the dir=
ect use of "::class", but the call to constant() is in a different namespac=
e, with different use statements=2E I'm not sure if use statements are even=
 available at runtime, but if they were, there would be no way of knowing t=
hat the context of the call to test() should be used, not the context where=
 it's defined=2E

Regards,
Hi Kevin,

--=20
Rowan Tommins
[IMSoP]