PHP da OOP da Zanjirlarda Xavfsiz Olish Operatori

Xavfsiz olish operatori ?-> chaqirish zanjirlarida qo'llanilishi mumkin. Keling, bir misol orqali ko'rib chiqaylik. Faraz qilaylik, bizda quyidagi klasslar mavjud:

php<?php
  class User {
    public $city = null;
  }
  
  class City {
    public function getName() {
      return 'shahar nomi';
    }
  }
?>

Faraz qilaylik, biz foydalanuvchi shahrini zanjir orqali olishni istaymiz:

php<?php
  $user = new User();
  $user->city = new City();
  
  echo $user->city->getName();
?>

Agar shahar null bo'lsa, bunday zanjirni chaqirish xatolikka olib keladi:

php<?php
  $user = new User();
  $user->city = null;
  
  echo $user->city->getName(); // xatolik
?>

Xatolikni oldini olish uchun biz xavfsiz olish operatoridan foydalanishimiz mumkin:

php<?php
  $user = new User();
  $user->city = null;
  
  echo $user->city?->getName();
?>

Endi faraz qilaylik, shahar ham null bo'lishi mumkin. Bunday holda biz xavfsiz olish operatorini ikki marta ishlatishimiz mumkin:

php<?php
  $user = null;
  
  echo $user?->city?->getName();
?>

php<?php
  class Employee {
    public $name;
    public $position;
    
    public function __construct($name, $position)
    {
      $this->name = $name;
      $this->position = $position;
    }
  }
  
  class Position {
    private $name;
    
    public function __construct($name)
    {
      $this->name = $name;
    }
    
    public function getName() {
      return $this->name;
    }
  }
  
  $position = new Position('dasturchi');
  $employee = new Employee('john', $position);
  
  echo $employee->position->getName();
?>