How to Access Parent Class Variables in PHP?

Access Parent Class Variable in PHP: A Comprehensive Guide

Accessing parent class variables in PHP is crucial for understanding inheritance and object-oriented programming concepts. In the given example below, we have two classes, A and B, with class A as the parent class and class B as the child class.

class A {
    private $aa;
    protected $bb = 'parent bb';
}

class B extends A {
    function childfunction() {
        echo parent::$bb; // Error: Undefined class constant 'bb'
    }
}

The issue arises when we attempt to access the protected variable (bb) of the parent class A from the child class B using parent::$bb. This results in a fatal error since $bb is defined as protected, which means it is accessible within the class itself and by subclasses, but not directly from outside the class.

Solution:

To resolve this issue, we can use $this keyword which refers to the current object:

echo $this->bb;

The $this keyword provides access to protected and private variables and methods within the current class, allowing us to display the value of the $bb variable in this case.

Additional Information: Using parent::

In addition to using $this, we can also utilize the parent:: syntax to access variables and methods from the parent class. Unlike $this, parent:: is used when we want to either override or extend functionality from the parent class.

For example, suppose we want to create a new class that extends the Airplane class and adds a navigator property:

class Airplane {
    private $pilot;
    function __construct($pilot) {
        $this->pilot = $pilot;
    }
}

class Bomber extends Airplane {
    private $navigator;
    function __construct($pilot, $navigator) {
        parent::__construct($pilot); // Call parent constructor
        $this->navigator = $navigator;
    }
}

In this scenario, we override the __construct() method in the Bomber class, but we still use parent::__construct() to ensure that the original functionality of the Airplane class is maintained.

Understanding the difference between $this and parent:: is essential for effectively leveraging inheritance in PHP and creating robust and maintainable code.

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