<?php
abstract class A
{
    abstract protected function _protected();
}

class B extends A
{
    protected function _protected()
    {
        echo 'protected B';
    }
}

class C extends A
{
    function test()
    {
        (new B())->_protected();
    }

    protected function _protected()
    {
        echo 'protected C';
    }
}

(new C())->test();

class A
{
	public function test(B $b)
	{
		return $b->_protect();
	}
}

class B extends A
{
	protected function _protect(){
		return '_protect';
	}
}

$a = new A();
print $a->test(new B());// '_protect'