PHP 8.3 Typed Class Constants - Closures

Question

This article https://php.watch/versions/8.3/typed-constants#supported_types affirms that PHP 8.3 allows us to declare typed constants of Closure type.

But I could not find any reference on how to do it. Is it a mistake, or is there the possibility to have closures as constants? How can it be done?

I tried to guess the syntax on my own, but with no results:

class ClassWithTypedConstants
{
    public const int INTEGER = 1;
    public const int|string INTEGER_OR_STRING = 1;
    public const \Closure CLOSURE = () => {};
}

Answer 1

The const keyword only supports limited expressions, but the define function supports arbitrary expressons, so you can use it to define a constant first and then assign it to a class constant.

define('CL', function () { echo "hello\n"; });

class Foo
{
    public const \Closure CL = CL;
}

This doesn't make much sense, I agree with the article just pointing out that Closure is an allowed type.

BTW if you try to invoke the constant, you need to wrap it in parenthesis.

(Foo::CL)();