What happens in this code block during php oop?
<?php
       class xyz {
        public function foo(Request $request){
          //some code
        }
       }

<?php
// An example class
class MyClass
{
    /**
     * A test function
     *
     * First parameter must be an object of type OtherClass
     */
    public function test(OtherClass $otherclass) {
        echo $otherclass->var;
    }


    /**
     * Another test function
     *
     * First parameter must be an array
     */
    public function test_array(array $input_array) {
        print_r($input_array);
    }
}

// Another example class
class OtherClass {
    public $var = 'Hello World';
}

<?php
// An instance of each class
$myclass = new MyClass;
$otherclass = new OtherClass;

// Fatal Error: Argument 1 must be an object of class OtherClass
$myclass->test('hello');

// Fatal Error: Argument 1 must be an instance of OtherClass
$foo = new stdClass;
$myclass->test($foo);

// Fatal Error: Argument 1 must not be null
$myclass->test(null);

// Works: Prints Hello World
$myclass->test($otherclass);

// Fatal Error: Argument 1 must be an array
$myclass->test_array('a string');

// Works: Prints the array
$myclass->test_array(array('a', 'b', 'c'));
?>

<?php
    class User
    {
        private $username;

        public function get_username()
        {
            return $this->username;
        }
    }

    class xyz()
    {
        public function foo(User $currentUser)
        {
            $currentUser->get_username();
        }
    }

    $x = new xyz();

    $u = new User();
    $x->foo($u);           // That will not produce any error because we pass an Object argument of type User

    $name = "my_name";
    $x->foo($name);        // This will produce an error because we pass a wrong type of argument
?>

$request instanceof Request == true