PHP __toString() bubble test

test.php

<?php

class Foo {
    public $bar;

	public function __construct()
	{
		$this->bar = new Bar;
	}

	public function __toString()
	{
		return $this->bar;
	}
}

class Bar {
	public $value;

	public function __construct()
	{
		$this->value = "Hello";
	}

	public function __toString()
	{
		return $this->value;
	}
}

var_dump((string) new Foo);
exit;

Expected output is the value of $this->bar->value, but actually throws Catchable fatal error: Method Foo::__toString() must return a string value.

Can be fixed by changing the Foo::__toString() to return (string) $this->bar explicitly.