PHP how to define and call a parent constructor from a child class

PHP inheritance features allow you to define a constructor method in a parent class.

The constructor can then be called from the child class with the parent::__construct(arguments) syntax.

When the child class doesn’t have a constructor, the parent constructor will be called automatically.

For example, suppose you have a Vehicle class as shown below:

class Vehicle {
    function __construct() {
        print "Constructing a vehicle";
    }
}

Suppose you have a Car class that extends the Vehicle class as shown below:

class Car extends Vehicle {
    function start() {
        print "Starting the car";
    }
}

When you create a Car object, the Vehicle constructor gets called automatically:

$car = new Car();
// 👆 prints: Constructing a vehicle

But if the child class has a constructor, then the parent constructor won’t be called automatically:

<?php
class Vehicle {
    function __construct() {
        print "Constructing a vehicle";
    }
}

class Car extends Vehicle {
    function __construct() {
        print "Constructing a car";
    }
}

$car = new Car();
// 👆 Constructing a car

To call the parent constructor in a child constructor, you need to use parent::__construct(arguments) syntax.

See the example below:

class Vehicle {
    function __construct() {
        print "Constructing a vehicle";
    }
}

class Car extends Vehicle {
    function __construct() {
        parent::__construct();
        print "\nConstructing a car";
    }
}

$car = new Car();

The output of the code above will be:

Constructing a vehicle
Constructing a car

As you can see, now the parent Vehicle constructor gets called from the child Car constructor.

When the constructor method requires argument(s), then you need to pass them when initializing the object or calling the parent constructor manually.

Now you’ve learned how to define and call a parent constructor in a child constructor using PHP. Nice work! 👍