How to access array elements?

Question

PHP

Friends, maybe someone knows
why we sometimes access array keys through square brackets: $locations[ $menu_name ]
and sometimes like this: $menu_item->url (inside the loop)
I get confused all the time.
Here is an example code from wp-kama.ru. I understand what it does, but these calls to properties are confused all the time.

// Получим элементы меню на основе параметра $menu_name (тоже что и 'theme_location' или 'menu' в аргументах wp_nav_menu)
// Этот код - основа функции wp_nav_menu, где получается ID меню из слага

$menu_name = 'custom_menu_slug';
$locations = get_nav_menu_locations();

if( $locations && isset($locations[ $menu_name ]) ){
  $menu = wp_get_nav_menu_object( $locations[ $menu_name ] ); // получаем меню

  $menu_items = wp_get_nav_menu_items( $menu ); // получаем элементы меню

  // создаем список
  $menu_list = '<ul id="menu-' . $menu_name . '">';

  foreach ( (array) $menu_items as $key => $menu_item ){
    $menu_list .= '<li><a href="' . $menu_item->url . '">' . $menu_item->title . '</a></li>';
  }

  $menu_list .= '</ul>';
}
else 
  $menu_list = '<ul><li>Меню "' . $menu_name . '" не определено.</li></ul>';

Answer 1

$locations[ $menu_name ]- array
$menu_item->url- object
The concept element refers to an array, property - to an object .

Answer 2

I will add that in addition to full-fledged classes, there is also StdClass - an empty default class out of the box, to which properties can be assigned.

$o = new \StdClass;
$o->prop1 = '123123';
$o->prop2 = 'xxxxxx';

It can be converted to an array:

$o = (array)$o;
echo $o['prop1'];

And any array can be converted to StdClass:

$arr = ['test1' => 1, 'test2' => 2];
$o = (object)$arr;
echo $o->test1;

Answer 3

You don't know OOP if you ask this question
How to access the elements of an array?
$numbers = array(1,2,3);
echo $numbers[0]; // prints 1
How to access objects?
class Numbers {
public $one = 1;
public $two = 2;
public $three = 3;
}
$object = new Numbers();
echo $object->one; // prints 1