The parent:: Keyword

Part of the Object Oriented Programming section of Coddy's PHP journey — lesson 22 of 91.

When a child class inherits from a parent, sometimes you need to access the parent's methods or properties directly. The parent:: keyword lets you call the parent class's implementation from within the child class.

This is especially useful in constructors when the child needs to initialize the parent's properties while also setting up its own:

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

class Dog extends Animal {
    public $breed;
    
    public function __construct($name, $breed) {
        parent::__construct($name);
        $this->breed = $breed;
    }
    
    public function describe() {
        return "$this->name is a $this->breed";
    }
}

$dog = new Dog("Max", "Labrador");
echo $dog->describe();

Output:

Max is a Labrador

By calling parent::__construct($name), the child class reuses the parent's initialization logic instead of duplicating it. Without this call, the $name property would never be set.

You can use parent:: to call any parent method, not just constructors. This becomes particularly important when you want to extend a method's behavior rather than completely replace it.

Key Point: The parent:: keyword provides a way to access the parent class's implementation. It's essential for proper constructor chaining and for building upon inherited functionality rather than rewriting it.

Challenge

Easy

Let's build a product catalog system that demonstrates how child classes can extend parent functionality using the parent:: keyword to properly chain constructors and build upon inherited methods.

You'll organize your code across three files:

Product.php — Define a Product class that serves as the base for all products. It should have public properties $name and $price. The constructor accepts a name and price, setting both properties. Include a getDetails() method that returns "[name]: $[price]".
ElectronicProduct.php — Define an ElectronicProduct class that extends Product. Include the Product file at the top. This class adds a $warranty property (in months). The constructor should accept name, price, and warranty — use parent::__construct() to initialize the name and price through the parent, then set the warranty yourself. Create a getDetails() method that builds upon the parent's implementation: call parent::getDetails() and append " (Warranty: [warranty] months)" to it.
main.php — Include the ElectronicProduct file. You'll receive three inputs: the product name, price (as a string to convert to a float), and warranty period (as a string to convert to an integer). Create an ElectronicProduct with these values and print the result of calling getDetails().

This challenge shows the real power of parent:: — not just for constructor chaining, but also for extending method behavior. Your ElectronicProduct reuses the parent's formatting logic and adds its own details on top, avoiding code duplication while creating richer output.

Cheat sheet

The parent:: keyword allows a child class to access methods and properties from its parent class.

Use parent::__construct() to call the parent's constructor from the child class:

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

class Dog extends Animal {
    public $breed;
    
    public function __construct($name, $breed) {
        parent::__construct($name);
        $this->breed = $breed;
    }
}

You can also use parent:: to call any parent method and extend its behavior:

<?php
class Animal {
    public function describe() {
        return "This is an animal";
    }
}

class Dog extends Animal {
    public function describe() {
        return parent::describe() . " and it's a dog";
    }
}

This approach allows child classes to reuse parent logic instead of duplicating code, enabling proper constructor chaining and method extension.

Try it yourself

<?php
require_once 'ElectronicProduct.php';

// Read inputs
$name = trim(fgets(STDIN));
$price = floatval(trim(fgets(STDIN)));
$warranty = intval(trim(fgets(STDIN)));

// TODO: Create an ElectronicProduct with the input values
// and print the result of calling getDetails()

?>

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

The parent:: Keyword

Cheat sheet

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