Objects Inside Classes in OOP in PHP

Classes can use objects of other classes. Let's look at an example. Suppose we want to create a user with a first name and last name, and also a city where they live. Suppose we have the following class for a city:

php<?php
  class City {
    public $name;
    
    public function __construct($name) {
      $this->name = $name;
    }
  }
?>

We will pass the first name, last name, and city as parameters to the constructor:

php<?php
  class User {
    public $name;
    public $surn;
    public $city;
    
    public function __construct($name, $surn, $city) {
      $this->name = $name;
      $this->surn = $surn;
      $this->city = $city;
    }
  }
?>

In this case, the first and last name will be strings, but the city will be an object of its own separate class:

php<?php
  $city = new City('luis');
  $user = new User('john', 'smit', $city);
?>

Let's output our user's first name:

php<?php
  echo $user->name;
?>

And now let's output the city name for our user:

php<?php
  echo $user->city->name;
?>

php<?php
  class Employee {
    public $name;
    public $position;
    public $department;
  
    public function __construct($name, $position, $department) {
      $this->name = $name;
      $this->position = $position;
      $this->department = $department;
    }
  }
?>