Can't understand PHP code snippet using call_user_func

Here is the snippet:

class A
{
    static function bar()
    {
        echo get_called_class(), "\n";
    }

}


class B extends A
{
    static function foo()
    {
        call_user_func(['parent', 'bar']);// B why?
        call_user_func([parent::class, 'bar']); // A
        call_user_func(parent::class . '::bar');// A

    }

}

• Why does call_user_func(['parent', 'bar']) return B?
• What is the difference between ['parent', 'bar'] and [parent::class, 'bar']?

With the latest PHP version you may see this deprecation message:

> Deprecated: Use of "parent" in callables is deprecated

And some more details of the deprecation you can find already here:

• PHP RFC: Deprecate partially supported callables

I don't find this easy to answer, but this is how I understand it: As "parent" is a string only and a generic name its meaning (which concrete class) depends on context.

I suspect get_called_class() is therefore incompatible with it and can't resolve the class context as you have expected it.

When you use parent::class PHP can resolve the context properly to the concrete class name, therefore using it with call_user_func() does not have this ambiguity or context problem.