Opereta ya Uchimbaji Salama katika Minyororo katika OOP katika PHP

Opereta ya uchimbaji salama ?-> inaweza kutumiwa katika minyororo ya miito. Tuangalie kwa mfano. Tuchukulie tuna madarasa yafuatayo:

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

Tuchukulie tunataka kupata mji wa mtumiaji kupitia mnyororo:

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

Iwapo mji unakuwa sawa na null, basi utoaji wa mnyororo kama huo utasababisha hitilafu:

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

Ili kukandamiza hitilafu, tunaweza kutumia opereta ya uchimbaji salama:

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

Tuchukulie sasa mji pia unaweza kuwa null. Katika hali hii tunaweza kutumia opereta ya uchimbaji salama mara mbili:

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('developer');
  $employee = new Employee('john', $position);
  
  echo $employee->position->getName();
?>