How to Access Parent Class Variables in PHP

Access Parent Class Variable in PHP

In object-oriented programming, accessing the parent class variable within a child class can present a challenge. Consider the code below:

<code class="php">class A {
    private $aa;
    protected $bb = 'parent bb';

    // ...
}

class B extends A {
    function childfunction() {
        echo parent::$bb; // Fatal error: Undefined class constant 'bb' 
    }
}
</code>

Attempting to access the $bb variable using parent::$bb results in an error. This is because the variable is protected, and protected variables are only accessible within the class and its child classes.

Solution: Using $this->bb

To access the $bb variable in the child class correctly, use $this->bb. This syntax refers to the current object's instance variable, which includes the inherited variables from the parent class.

<code class="php">echo $this->bb;</code>

The $bb variable is inherited and is not private, so it is part of the current object and can be accessed using the $this keyword.

Additional Information

For situations where you need to modify the behavior of a method from the parent class, use parent::. For example, consider the following:

<code class="php">class Airplane {
    private $pilot;

    public function __construct( $pilot ) {
        $this->pilot = $pilot;
    }
}

class Bomber extends Airplane {
    private $navigator;

    public function __construct( $pilot, $navigator ) {
        $this->navigator = $navigator;

        parent::__construct( $pilot ); // Assign to this->pilot
    }
}</code>

Here, parent:: extends the constructor from the Airplane class to add the $navigator variable. This allows you to follow the DRY principle while providing desired functionality.

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